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Robyn's Pond Talk Page

Last Updated: 2/19/14

This is a new page that includes information that I discussed via e-mail with other pond keepers. If I feel it is important but do not know where to place it, I will add it here. Most of this page is from e-mails I have with Christine as she always knows the best questions to ask!

Discussion with Christine - covers plants, algae, decomposition, bacteria, chemical processes in ponds, and a koi parasite

Overflow Designs

Discussion with Christine 2 - covers various aspects of algae and its benefits

Discussion with Christine 3 - covers why fresh water spawns algae, koi clay, water changes

Discussion with Christine 4 - covers heterotrophic and autotrophic bacteria

Discussion with Christine 5 - on gravel/rocks on pond bottoms

Discussion with Christine

The following is an e-mail discussion between myself and Christine from March 26 to March 30 of 2001. I thought that some other pond keepers might learn from what I had to say. Advanced watergardeners (I am not!) are free to disagree! I am probably not 100% correct.

Christine is Christine Savage of Pine Creek Hollow Fish Farm. Check her web site out at pinecreek. She breeds koi in Ontario, Canada and sells other pond plants and animals as well.

1. Christine asked some questions in two separate e-mails that I answer in Number 2 and Number 3 below. I did not print these e-mails so I cannot quote from them. I do not remember exactly what she said.

2. Robyn: ...As for algae consuming ammonia and nitrite, this is what I've heard. Most pond keepers say that both algae and higher plants consume the end product of the nitrogen cycle which is nitrate. But, many of the more advanced aquarium plant keepers and watergardeners say that in fact, plants (algae is a plant but some will say otherwise) PREFER to consume ammonia. That means that while they will use nitrate, if ammonia is there, they will take that up first. I'm not sure about nitrite; I don't think plants use that. So, what aquarium plant keepers are saying especially is that in heavily planted tanks and ponds, you don't want nitrifying bacteria because they compete with plants for the ammonia! They say, don't have a biological filter in a heavily planted tank. Now, the actuality of it is that most people have ponds with lots of fish. These fish produce too much ammonia for even a burst of algae to consume. So, you need the nitrogen cycle to continue to render the excess ammonia to nitrate which is less toxic by thousands of times. Then, if the plants are still "hungry," they can use the nitrate produced. If you have a super efficient and active biofilter, then the bacteria will get most of the ammonia, and the plants and algae will be left feeding on the nitrate. This is confusing but for us pond keepers, it basically means that we just want a lot of plants and if we have a lot of fish, we still need a biofilter. If we have just a few fish in a well planted pond, a biofilter is not necessary although it will occur naturally on all surfaces of the pond. Aeration of some sort is still needed in a heavily planted pond or one having an algae bloom because at night, the oxygen levels will plummet. One thing that can be noticed in ponds like mine that have a large biofilter followed by a stand of watercress and water celery in my case, is that the floating plants in the rest of the pond often turn yellow. They don't get enough ammonia or nitrate. At the same time, hair algae also grows with the water celery because there's still enough nutrients there. BTW, I've found that watercress and water celery are the best vegetative filtration for my pond in Zone 6/7. They are up and filtering now while everything else is dormant except the fish!

3. Robyn: Ok, when rotten or dead vegetation and leaves fall down to the bottom, microorganisms and bacteria begin to act on them to break them down and eat them. Over time, the material becomes slimy and then falls apart to mulm. There are two types of bacteria, aerobic and anaerobic. Aerobic bacteria require oxygen. These include the ones in a biological filter doing the nitrogen cycle. A biofilter thus removes oxygen from the pond, and those bacteria will die when there's not enough oxygen. When the oxygen level drops too low, the anaerobic bacteria kick in. Those produce methane gas and hydrogen sulfide gas as byproducts. This happens in stagnant ponds. They will stink like rotten eggs (hydrogen sulfide). So, in a healthy pond, when the plant material falls, the aerobic bacteria get to work and use up a lot of oxygen on the bottom where the levels are the lowest. The poor fish may not have enough oxygen and will come to the top and suck air. When the oxygen gets too low for the aerobic bacteria, then the "bad" anaerobic bacteria kick in. Not only does this make the pond stink, but both methane and hydrogen sulfide will kill fish if the concentrations are too high.

For dead vegetation to cause these problems, you need a good amount of it. In the fall in areas with trees, the leaves will be enough. They may not rot until spring though when the fish may suffocate. What about natural ponds? Well, they have few fish and often water flowing through the system constantly replenishing the oxygen and changing the water. Natural waters may have die offs from algae blooms (oxygen plummets at night) or after the algae die as the bacteria use too much oxygen to digest the dead algae. Really anytime you add something to an aquarium or body of water that kills off algae, plants, fish, snails, or anything else, the decomposition of that material will consume oxygen. That's why it is best to remove the species in question or to slowly kill it off over time. I prefer prevention myself! I use barley straw, vegetative filtration, and CSA. CSA ( I think (note added 10/2/01, CSA site is down, same product may be that sold as BZT Aquaculture at this site (which may no longer work) or better yet United-Tech, Inc. directly.)) is dried bacteria (and enzymes) that compete with the anaerobic bacteria but do not produce methane or hydrogen sulfide. They eat the debris up without depriving the fish of oxygen or adding methane or hydrogen sulfide (I'm not sure how they do it!). This was a very good question. It took me a long time to answer so I think I will add this information to my web site soon! Thanks!

4. Christine: ...So, let me see if I have this it safe to say, that suspended algae not only thrives on nitrates but on ammonia directly, and therefore green water can be found in systems with poor water quality too? And that string and surface algae thrive more on the final product of the nitrogen cycle and are found most often in ponds with good water quality? And, that aerobic bacteria compete directly with suspended algae, as both consume ammonia, so the bacteria robs the suspended algae of nutrients...whereas the bacteria has no direct affect on string and surface algae. The only thing that will keep these to a minimum is plants which will compete with the algae for the nutrients from the nitrogen cycle? Does this sound right? I've never had a problem with algae. The pond that our koi are raised in is a very big natural clay pond. Behind the pond is a approx. 25 foot biological filter. In the final chamber, we keep the seasons supply of water hyacinths and water lettuce. They grow to sizes that people can not believe!...Because the koi pond is so big, we don't have a lot of plants in the water, so those hyacinths are keeping the water in the pond without a lot of nutrients, so there is never more than an average amount of surface algae which my koi (and there's a lot of them) adore! Plus the fact that the water is always full of suspended clay particles makes it harder for the sun to penetrate the depths and I think that keeps the algae at bay....I want to be sure I repeat the right thing to people, because customers hear so many different things from people they get very flustered. They just want someone to give them the right answer. And I think I know quite a bit, but I will never stop learning! (Note from Robyn while transcribing this: I never stop learning either! Customers should be so lucky as to find someone like Christine who knows her stuff! Few people are around to give customers those right answers.).

5. Robyn: I did not print out my response but this is what I think I said. I do not think there is much difference between the different kinds of algae as far as how well they use ammonia or nitrate. Bacteria may "compete" with any algae or plant for that matter. It does seem that healthier ponds have more attached and hair algae in relation to their suspended algae. Suspended algae, being directly in the water, are able to take up nutrients faster and reproduce faster than other algae or plants.

6. Christine: ...Suppose a person has a very small pond, is not using biological filtration, so is not depending on nitrifying bacteria to remove the ammonia, and is depending on chemical filtration...lets say...activated carbon. They are getting a buildup of waste on the pond floor. But, any forming ammonia is being taken out via the carbon. Therefore, there will be no bacteria using up tons of oxygen trying to consume the ammonia. In this case, would the silt on the pond floor not cause a problem? If the nitrifying bacteria are not using up oxygen to try and break down this overload, then there would be no anaerobic bacteria thriving in the silt. So would this silty waste then NOT cause a problem in that pond?...

7. Robyn: Silt and mulm are two different things. Silt is inorganic rock particles. Mulm is the "black gold" of pond keeping, the stinking sludge. Any pond, irregardless of size, will have a biofilter! It's all over the liner, the rocks, the plants, and anything that's wet. Those bacteria will uptake some of the ammonia from the water. Carbon can take up ammonia but it's not especially good at it. After a short time (it depends on the number of fish, etc.), the carbon will have all its active sites filled up. It won't be able to take any more and may even leach some back out (if it finds other chemicals, etc. that it wants to exchange for ammonia). Zeolite (white rock often sold with carbon as ammo-carb, etc.) is much better at taking up ammonia. I add some to my filters sometimes when they're starting up to absorb ammonia. So, your little pond without a biofilter really has one and nitrifying bacteria will be present. Any mulm will still be attacked by bacteria. I guess my previous e-mail was not clear; there are more species of aerobic bacteria than just nitrifying bacteria. There are all sorts of bacteria and also microorganisms that will compete to digest that debris. If a pond could be devoid of nitrifying bacteria, that would in fact make the debris even more dangerous as the other forms of bacteria would do better and they are problematic.

8. Christine: Ok, so several kinds of aerobic bacteria and microorganisms work to break down debris...and nitrifying bacteria work specifically on turning ammonia to nitrate. So all aerobic bacteria use a lot of oxygen in the breakdown...not just the nitrifying bacteria? And nitrifying bacteria will thrive naturally in a pond...we are just encouraging a large population to thrive in our biofilters to handle the excess load of fish in particular? Does that sound about right? And I'm still a little confused about silt and mulm. Is one of these the same as detritus? Which of these is the one that is made up of rotting excess food, solid waste, plant bits, and through the aerobic bacteria working feverishly to break it down and hence using so much oxygen, can deplete the oxygen and encourage the growth of anaerobic bacteria? Which one is good?...

9. Robyn: It all sounds right to me! Detritus is debris. It may not be fully decomposed but is made up of leaves, plants parts, dead animals, bacteria, etc. After the bacteria use enzymes to digest the detritus, it becomes fine; this is mulm (which may be further digested over time). Mulm is digested and makes a good fertilizer for land plants (it usually is thick, black, stinks, and stains your hands). Silt is a term used for a fine layer or inorganic material; in other words, it's sand, dirt, and fine particles of rock. For example, my pond has silt in it from the granite particles that come out of my well. It also has mulm from the plant debris that rotted over winter. I usually use detritus and mulm interchangeably but really detritus still contains hole parts of plants and animals that can be digested while mulm is pretty much done being digested. If you have silt in your pond, it's no problem unless it contains fine clay particles that can make a pond cloudy. This would be like dirt washing into the pond after a rain (assuming the dirt were all inorganic which means non-living when it really has microbes in it too). Inorganic is not always good as ammonia, nitrite, nitrate, phosphate, etc. are inorganic too. If you have mulm in your pond, it means that the pond is functioning well as the debris or detritus was digested well. You want to remove detritus as much as possible but you'll always miss some so it's better that there are some bacteria to digest it. Yes, they will use oxygen and/or produce methane or hydrogen sulfide but it's all about the relative amounts. Some is good; too much is bad. I always leave some leaves (really because I can't get them all!) For the frogs to sleep under over winter and the pond insects, snails, tadpoles, etc. to munch on.

10. Christine: Ok, Robyn, I think I have everything pretty much understood now...I just have 2 more questions....My large koi pond (about 1/4 acre) is now melting, and there is algae on the surface in the open spots that wasn't there in the fall. I have read that algae on the bottom of the pond will float on very warm days when it gives off plenty of oxygen, and the oxygen gets trapped in the algae itself, making it buoyant, and it will float to the top. Have you heard of this? We did have quite a warm spell last week, so, I'm wondering if this is what might have happened? What kind of algae is this slimy stuff that floats on the surface (and apparently is on the bottom too)? And, what exactly does happen to algae that is in the water in the fall? Does it go dormant? Does the wonderful brownish algae on the sides of the pond and pots go dormant, or does it die off in the winter? I always assumed that it dies in the winter, but I think I'm wrong. Is surface algae also a filamentous algae? Is the surface algae on pots and the sides of the pond, brownish in color because it is a good area for nitrifying bacteria? Is this bacteria giving it this colour?

Finally, the methane gas that's given off in areas where there is it always given off in such areas? Or, is it only when there is anaerobic bacteria at work? (I think you said that this bacteria gives off the methane and hydrogen sulfide as by product?) And the bacteria and microorganisms that immediately start to work on waste in the pond are all aerobic, right? It's not just the nitrifying bacteria that's aerobic.

I think that covers pretty much everything...although if I think of anything else (and I'm sure I will), I'll let you know! I think I deserve some sort of diploma for passing this Robyn's Pond Course! Thanks again...Christine.

11. Robyn: Yes, algae that is giving off a lot of oxygen will float up. I would guess it's (the "slimy stuff") a type of hair algae or perhaps a slime algae. I'm not an expert on algae nomenclature. There are thousands of algae species. The hair algae does well in cooler weather. Hair algae can be slimy when it gets mixed with other species of algae. The best thing for hair algae is to remove what you can and use the natural algae preventions we've discussed.

(About whether algae dies or goes dormant) Obviously, if all the algae died, it would not return unless brought on the feet of a migrating bird from a warmer climate or something. Most of the algae dies but a few cells remain alive and dormant (non-reproducing) over the winter. All it takes is heat and light, and the cells multiple quickly. Hair algae will remain active all winter as long as it doesn't freeze solid. It will grow under ice. True brown algae are diatoms and not algae. If your attached green algae were mixed with dirt, I suppose ti would look like brown algae. I classify algae into these groups but it's not 100% legitimate to do this: suspended, attached green/surface, hair/slime/brush/filamentous, brown (diatoms), and blue-green (cyanobacteria, rare in ponds). Floating surface algae is probably hair or slime algae that came up. If by surface algae, you mean what I call attached green algae, then that is not a hair algae. Brown algae are diatoms and like lower levels of light (than green algae). The sides of pots are usually more shaded and brown algae will grow there. (I forgot to answer about nitrifying bacteria coloring the pots brown. The bacteria are mostly like a slimy film that itself does not have much color. When debris and algae get trapped into it, it may be many color choices. Most likely, I would think her "brown" pots have a mix of bacteria, brown algae, and dirt or debris. My pots in shady areas have this; it can just be called an algae, bacterial, slime layer.) In full sun, the sides of pots will be covered with hair algae (which also attaches) and attached green surface algae (which is a very thin layer). Have you read my aquarium algae page which goes into more of this type of info? (click here).

There are always many species of both aerobic and anaerobic bacteria present. They're always there. It's all about relative numbers. If the oxygen levels go down, and there's lots of debris, then the anaerobic bacteria proliferate, and methane is released. In a healthy pond, there will be small amounts released in low oxygen, high debris areas of the pond (the floor) but not enough to do any harm. All sorts of micro-critters including bacteria, funguses, small insects, worms, etc. go to work on debris that falls in a well oxygenated area (near the surface, in a waterfall, etc.)....

12. Follow Up from Christine regarding a koi parasite:

"...I know you have koi....there is a parasite that can infest your looks a lot like a fungus. Most people will run out and buy some sort of drug to treat the fungus. If your fish is feeding well and is normally is probably not a fungus! A fish is pretty much close to death before it will get fungus (according to Doc Johnson...KoiVet). I brought in a fish this year that looked just dreadful! White stuff resembling fungus all over one side. I thought for sure that it would die, but I remembered what Doc Johnson had said, and I put him in a sick tank with a .3% salt solution (that's 3 teaspoons per gallon) for just over a week. Absolutely amazing!!! Every day I would see bits of this stuff falling off. Now he is perfect!! I STRONGLY believe in salting koi in spring to kill off any parasites (won't do anything for anchor worm or gill flukes though). Anyways, this parasite is called Epistylis. If I hadn't seen it with my own eyes, I wouldn't have believed it! Someone may euthanize a prized fish thinking it has a terrible fungus and will die...but it could be this parasite!..."

Overflow Designs

I mention problems with my pond's overflow on my pond problems page. It is important to have an overflow on most any pond. Linda sent me this e-mail after reading my web site with some overflow designs. While I will not use them as my overflows work well enough, they may be useful to others.

"Hi, Robyn, Thanks for all the info on what to avoid in pond making. We dug our own and it took all summer, 2300 gal. It's got an overflow design that may help you out. We've done two versions in two ponds.

Version one: Dig a round hole about 1.5 feet from the pond edge so as not to weaken the pond edge. Dig it the shape of a 5 gallon bucket. If this is located in your bog garden, so much the better, but it doesn't have to be. Saw the bottom off a 5 gal bucket and slide it in the hole so the top is even with the soil level. Place 2 or 3 inches of large gravel in the bottom on top of the dirt. Now place a plastic gallon pot upside down in the hole so the bottom is facing up. Put a plastic quart yogurt or quart cottage cheese container right side up on the pot base like a pail. Fill the yogurt 'pail' with water and start a siphon with a section of hose. (Submerge the hose in the pond until all bubbles stop. Hold thumbs over both ends. Place one end in the pond and the other in the yogurt 'pail.' Release thumbs.) The pond level will maintain at the level of the yogurt pail top. Raise the level of the pond by shimming up the pail or lower it by removing some of the gravel so the pail is lower.

Our version two: We dug a 5' hole to take care of under the pond ground water. We lined the hole with two plastic garbage cans, one above the other. A sump pump pumps water into a drain line to the street. But back to the overflow. We glued an end cap on a 4" diameter piece of ABS pipe about a foot long. We hang this in the hole (like a bucket) with the hose inserted in it and in the pond, again repeating the siphon. We raise or lower the pond level by raising or lowering the ABS pipe which hangs by a light rope. The pond level stays the level of the top of the ABS pipe.

These two version offer infinite control of your pond level. We did this because our ponds looked like they were drowning (water level too high) after a rain. After reading this, I can appreciate the phrase, 'A picture is worth a thousand words.'..."

Discussion with Christine 2

This discussion occurred between 2/19/02 and 2/20/02 with the same Christine as before.

1. Christine: Hi Robyn!...I need to pick your brain once again! In every piece of literature I read, it states that, the smooth algae growth on the walls, bottoms, pots and all other surfaces of the pond, is a sign of good pond health, and good water quality. We all know this, but in NO book that I can find, does it say why! What makes this algae a sign of good pond quality? I have my theories, but they are only that. I'd like to have a good solid answer. So I thought maybe you would know! My theory is....nitrifying bacteria hangs out on all of these same surfaces, which in itself is good. So, if there is highly concentrated amounts of bacteria on these surfaces, they are totally consuming any ammonia in the water, (and the pond therefore is not overstocked or fish being overfed) and the small amount of nitrate that is being produced is being consumed by the algae that is right there on these same surfaces to grab it immediately. In other words there is just the right amount of nutrients in the water, and if the algae wants to thrive, it needs to be right where the action is, because there will be very little excess in the water. And it can also continue to filter the water by it's very existence! The water plants will take what they need either by consuming the ammonia, or the nitrate. But the water plants aren't converting the ammonia to nitrate, like the bacteria is, so instead of a lot of algae thru the water and near the plants, the algae is found where it knows it can feed off the by product of the ammonia consumption by the bacteria.'s probably something much simpler than this, or maybe there is no explanation...maybe this algae just prefers to grow in good quality water! But because of where it's growing, I feel there must be some explanation. Last year I had a few people come to me who said that people have told them it's bad to have that algae and you should scrub down your pond and empty it!! Robyn..can you believe this!! So I told them," NO DON'T DO THAT!!!! THIS ALGAE IS A SIGN OF GOOD WATER QUALITY, PLUS IT CONTINUES TO FILTER THE WATER OF EXCESS NUTRIENTS!!" But I can never tell them exactly why it is good. I can't believe how some people call themselves professionals and give people advice and yet know absolutely nothing! And they are telling people stupid things to do like scrub down your pond and refill it! It's like these people who fill and refill their ponds over and over, and can't figure out why they always have green water! I tell them every time they refill that water with town water, algae is feeding on all sorts of things in that new water, not to mention that they're killing off their nitrifying bacteria every time, so if they have fish, there is no bacteria in there to consume the ammonia, so of course the algae is going to consume it and thrive like crazy!

Anyways, if you have any answers for me as to exactly why this algae is a sign of good water quality, please let me know so I can give an informed answer to my customers! Thanks Robyn, and I hope all is well!

2. Robyn: What you say makes sense. This is what I think (I don't know if I'm right!). Algae is a plant. Plants are good (to some extent) in that they filter the water, use ammonia and nitrate, etc. and provide oxygen during the day (but use it at night). That's the main reason. Having that algae is like having an extra big plant added to the pond with all its benefits. Then, like you said, there's lots of bacteria in there hanging with the algae. If you scrub off the algae, there goes more bacteria too. Plus, algae provides a haven for microorganisms to live. These critters feed larger critters and eventually the fish and especially feed snails, tadpoles, and fry. Without some surface algae in a pond, snails, tadpoles, and fry don't stand a chance of finding enough food. Another bonus of this algae is that it covers liners and pots and makes them look more natural.

It's the (name omitted so as not to make them mad) company that especially advocates a yearly complete clean out with harsh scrubbing to clean the pond. I NEVER scrub down a pond hard but I've done water changes and cleanings on my smaller ponds. I save water and put it back so there's no more than 50% changed at once. I have well water so no chlorine either. I've NEVER done a clean out of my 1800 gallon since it was made in 1997 except up to 10% water changes and using nets to collect debris on the bottom. By scrubbing down a pond, that sterilizes it, killing good bacteria, microorganisms, and other good stuff that you just tried so hard to grow in the first place. Doing large water changes not only poses a direct threat with city water from chlorine or chloramine but also removes lots of suspended critters like more good bacteria, cyclops, daphnia, fish fry, euglena, and all sorts of microorganisms AND it throws the water chemistry out of wack. It may add nitrate or phosphate in some cases or at least alter the pH, hardness, and salinity. Who takes advantage of this opportunity? Suspended algae, of course!

Guess I have to add this "talk" to my pond talk page (and here it is!) too since it's more info that someone somewhere might learn from. You ask great questions! I just wish I had more answers! Thanks.

3. Christine: Hi Again Robyn, I guess what I don't get is...what makes this particular algae a sign of good water quality, as opposed to say string or hair algae. All take up excess nutrients, thus filtering the water to keep it clean. But the attached algae is the typed that is always centered out as being a sign of good quality. Little critters live in free floating hair algae too. I had a lovely bunch of hair algae growing from the bottom of the pond to the surface last year. We had a really successful spawn last year (the most beautiful babies I have ever seen!). Anyways, that big beautiful clump was a favourite hang out of many of my babies! I'm just stuck on why the attached stuff (on pots liners) is centered out as the best. I guess I just assumed it had to have something to do with the fact that it grows on the same surfaces as is habitated by nitrifying bacteria....

4. Robyn: You are right, hair algae has its benefits too. Even more perhaps since fish love to spawn in it. However, since it tends to be more problematic by clogging filters, strangling plants, and such, it is not considered to be "good." I've found that my large pond has very little hair algae which means there's not enough nutrients left over once the tons of plants "feed." My smaller pond does get tons of hair algae (mostly in cool months) but it has less water movement and circulation. Anyway, everything is relative. There are negative and positive points to each type of algae (see the pond algae page). Even the dreaded suspended algae that makes water green is using nutrients, providing cover for animals, and food for microorganisms. I forgot to mention insect larvae and worms liking algae too.

Discussion with Christine 3

These discussions occurred on 12/21/02 (#1&2) and 1/18/03 (#3&4) with the same Christine as before.

1. Christine: ...When a newly filled-up pond (with no fish) turns green, what exactly in the fresh tap water is the algae thriving on? Many people will empty their ponds and refill just to try and get rid of it! I tell them that they are only repeating the problem! But I've never found out exactly what is so good about fresh tap water that algae loves so much? I'm assuming it is minerals, etc., but I'd love your take on it!...

2. Robyn: It depends on the water source. Well water usually has algae spores in it in spring. Plus, it often has high nitrates and phosphates (luckily mine doesn't). Algae LOVE nitrate and phosphate and thrive. City water (with chlorine) usually comes from reservoirs which of course are full of algae. If the chlorination isn't strong enough, you can get algae that might survive (but probably not the microorganisms). City water can also have nitrate and phosphate which cause the blooms as well. My well water is low in nitrate and phosphate so I don't get green water in my aquariums (they get 50% water changes weekly whereas my ponds get few water changes) but I do have high silicates (formica). Blue-green algae loves silica, hence my constant battles with it!

3. Christine asked about koi clay and minerals in ponds. I did not keep the e-mail so do not know the exact words.

4. Robyn: Most of the minerals that you're referring to are used in minute quantities by most fish. They're found naturally in clay and other dirts. Fish in natural-bottomed ponds have no problems. Fish in liner ponds may use up minerals over time if they are packed in tightly without enough water changes. Most ponds have some dirt run into them when it rains. My ponds get dirt running in plus the clay in the plant pots leaching when the koi root in them. You can buy koi clay which is now popular to add to liner koi ponds to provide the natural minerals and it's supposed to make them healthier and of better color. I don't think it would hurt. Most smaller ponds with a few fish won't have a problem. My pond gets water changes in the form of rain top which of course, is devoid of minerals. I top off the ponds a lot but my well water is very low in minerals and very soft. Water changes do put back trace minerals, etc. I think that water changes primary benefit is to dilute unseen waste chemicals, bring the pH and hardness back into better ranges, and replenish those minute trace elements as a last benefit of lesser importance. I swear by weekly 50% water changes in my aquariums but basically don't do many pond water changes (just top them off and rain dilutes sometimes) due to lack of time and water (we're on well and had the worst drought every last summer). My ponds are doing fine despite a lack of a water change regime so I'm afraid water changes may be overhiped for ponds. Anyway, I probably have no idea what I'm talking about after doing 12 hours of animal chores. Good night!

Discussion with Christine 4

1. Christine: some articles it is made to sound that nitrifying bacteria are heterotrophic. In other articles it appears that heterotrophic bacteria are different (the ones that begin the breakdown process to produce ammonia), and that nitrifying bacteria are autotrophic. And, that denitrifying bacteria are also heterotrophic. I'm confused!!! Any ideas?

2. Robyn: I don't know! You've lost me. I really don't know much about -trophic definitions. It doesn't matter really. There are good and bad bacteria, some need oxygen, some don't. Heterotrophic just means the bacteria is not self-sustaining and needs other organisms to live or food from decomposing stuff. Autotrophic organisms don't need outside food but they do use chemicals (ammonia, nitrite, etc.). According to one site, "nitrifying organisms are...obligate aerobic, chemo-litho-autotrophic."

Discussion with Christine 5

1. Christine: ...There seems to be a lot of debate on whether to line the bottom of a pond with stone. I think, that although it would be a wonderful big natural bio filter, it would make cleaning very difficult. Others say, that they get no build up of anything on the bottom when they use stone, because all the bacteria on the stone, takes care of all the waste. How can this be? You are still going to be left with mulm after decomposition, aren't you? I'd love your opinion.

2. Robyn: I'm not positive where I stand on this either. Have you seen my section on gravel at which lists the pros and cons? It is nearly impossible to clean the pea gravel in my ponds. Yet, the ponds aren't that dirty either. Plus, it looks nice and the small animals like snails and insects love it. I just redid my lotus tub pond which was 50 gallons of dirt topped with pea gravel and water. It was a total cesspool after 3 years but had no filter or pump and was impossible to really clean. When I stir the gravel in my big pond, I see some debris but it's not as bad as some would have you believe, and the smell is very little. So, it's really a matter of personal preference. Koi "experts" say you absolutely can't have gravel or all the fish will die which is false. (Name withheld) pond makers say you must have gravel or the pond will die which is false. Really, if you know what you're doing, either system can be successful. They just require different strategies. If you want a pristine pond though (I mean 100% debris free), don't add gravel, and if you want a 100% natural pond, add gravel. So, there's really no answer that fits everyone. This topic by the way is the one I've seen the most controversy about with each side swearing that you absolutely must either have gravel on the bottom or not have any. I have both kinds of ponds, and I just treat them a little different but they're all ok.

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