Water changes remove excess nitrates, heavy metals (which will just concentrate if the pond water is only replaced through evaporation), and organics not picked up by the filter. New water also brings in minerals that are essential to fish health.

Water changes are important in fish ponds to freshen the water as ccoombs has said. You need to know where you are at first off. Test your water for PH, ammonia, nitrites, nitrates, hardness. This will tell you how well your filtration system is handling the waste and ammonia excreted from your fish and the rotting debris from plants and such. And how much buffering capacity your pond has to prevent PH swings.

If your water tests within good limits then just a little freshening is needed. You must take into consideration your source water as well. My source water is high in phosphates, but also has calcium carbonate that helps buffer my pond water. So for me I need to have more plants to remove the phosphates and be careful not to add too much source water or I will have algae blooms.

If you have great water, excellent filtration, then perhaps 10% a month is all you need from spring till fall. If however your pond is lacking good filtration, overcrowded, ect then you will need to perform more frequent water changes until your filtration system is up to par.

Hope that helps.

Lisa

I have wondered this same question. I sometimes water our potted plants out of my pond and then top off with rain water or city water that has set for a few day. My reason for doing this was simply that the pond water had nutrients in it that is good for the plants. I didnÂt know there was any need for it otherwise.

Actually ponderpaul, rain water is not that great for koi, especially if it is run off from the roof. Years ago that might not have been true, but today rain is usually very acidic and may contain traces of many heavy metals. Also, the roof of a house collects many pollutants that end up in the pond if roof run-off is used. You are probably better off using city water that has been dechlorinated.

"I read often about doing 10,15 or 20% weekly water changes. I have not found the reasons for this explained yet. Could someone please tell me the benefits of doing this and the dangers of not? "

Melissa, mainly because it's really hard for a hobbyist to screw that up. Changing only 10% of your water will not effect the pH, or add enough chlorine/chloramine, to make a huge difference and possibly wipe out your pond.

Also keep in mind, 10% will only reduce anything you're trying to get of by 10% too. Same with 15% and 20%

Read what Lisa said. test, and realize there are some things you can't really test for.

Fish go through several 100% water changes between where they are raised, to where they are sold, to you. So obviously, it's not the fish, it's the water. But people that do that adjust their new water. It's hard for a pond owner to hold, adjust, in your case 1500 gal. of water in advance.

Think of it this way. Think of being shut up in your house for a weekend with the windows closed all weekend. By the end of that time the air is somewhat stale. Just think how good that fresh air is when you go outside. It is not that the air has poisons in it or that the O2 is low it is that contaminates are building up to a point where they bother us. The same can be said of the water the fish are in. They can't go outside to get fresh air they need you to give them fresh water.
Now the question is how much. It takes 8.9 times the volume of the pond to remove 99.95% of the contaminates by doing water changes. In other words if you have a 1000 gallon pond it will take 8900 gallons of water being added by water changes to get 99.95% of contaminate that were in the pond when you started changing the water. Any water changes are better then not changing any water. In a normally stocked pond the ideal amount is 100% of the pond volume per month done in the smallest amounts possible. So if it is possible to change water everyday then it would be 3% a day. If you can only change water once a week then it would be just less then 25%. I don't suggest changing more then 25% on a regular basis unless you are doing very often so the fish can get use to all the fresh water. On my personal pond I change 2.6% of the water on a daily basis.
Mike

i'm wondering if your water tests normal on everything do you still need to do water changes. i have had my pond for 2 months and i have not does anything except top it off a couple of time. and my water is testing good, although i do use ph buffer and stablizer because my well water is so soft i don't have a buffer to help maintiain the ph. the buffer stablizer has really helped my ph levels.

anyhow i was really wondering about the water changes. thanks so much for any help on this..

Water changes are imperative for the health and well-being of your fish. I have found, through many years of trial and error, that weekly water changes of 10% provide the least amount of stress and most amount of benefits for your pond fish. Koi on the other hand, will benefit more with more water changes and thrive with a flow through water system.
Werner's Ponds recommends the following: A 10% weekly water change and a one time 50% change in the fall of the year. Drain the water from the pond first and then add the fresh water. If you just overflow the pond, only 6% of the water will be changed, since you're flushing out fresh and old water. If your fish noticeably perk up after a water change, chances are your water changes are not frequent enough.
It's not the same as water changes and over time, pollutants will concentrate in your pond, changing your water quality to a deadly chemical soup. Heavy rains, unless they last for 24 hours, will serve to add further pollutants to your pond as well as changing the water chemistry, as rain is acidic and soft.
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Here is a link that might be useful: bailing

I'm kinda in the same boat here as loriques: "i'm wondering if your water tests normal on everything do you still need to do water changes."

I wonder that too as I keep my pond heavily planted and typically have zero nitrites and nitrates (I don't bother reading ammonia), with a steady pH too. Yes, I test it weekly so that's not a guess but a fact.

One thing I did some thinking about is how could a 10% change be effective when you're leaving 90% of whatever is bad in the water? If that took a week to build up then after week two you have 171% of whatever was bad left... I actually did a spreadsheet to see how much it would build up.

Yes, it does level out eventually at the point that one week of bad buildup is held in 10% of the water. So say your fish load leaves you with 10 ppm of nitrates after a week. If you do a weekly 10% change in 8 weeks you have 50 ppm, in 6 months you have over 80 pmm, and will eventually level out to between 90 and 100 ppm.

90 ppm just after the change and 100 ppm is just before. Basically, it builds to the percent of the water you change contains one week of bad water accumulation.

If you like formulas it's just: accumulation = (weekly addition) / (fraction of change)

For the rest of us here's a chart:

% water change - eventual buildup
0%................(dead fish)
5%................2000% (20 times)
10%...............1000% (10 times)
15%...............666% (6.6 times)
20%...............500% (5 times)
25%...............400% (4 times)

The only way to beat these numbers is to step up the rate of changes. If you do 2 a week you half the input per change and thus half the eventual build-up. The other way is to add lots of plants so the bad stuff gets eaten.

Water changes can cause stress, true. The changes in dissloved solids cause more stress then pH changes from some studies I've read. One way to alleviate that is a slower refill rather then a full open valve. It may take longer but it is a gradual and will cause less or no stress. If you are only doing 10% or less or even none you are opening yourself up for a crash eventually. Minimally algae blooms if nutrients are aloud to build. 25% a week is best more if you can swing it.

I realize after reading the posts, I will be doing a water change this weekend. I did not install a bottom drain, can I siphon off the top, siphon from the bottom and hope some "debris" comes out with it? How do I keep the fish away from the siphon? Sorry for the basic questions, here. I just would rather learn the easy way as opposed to the hard way if at all possible.

What are you using to siphon? You can put a valve on the siphon to restrict flow. You can put a strainer on the end just smaller then your smallest fish. A possibility down the road is a retro-fit bottom drain. They are for existing ponds without BD's or for those who are leary of installing one.

I do partial water changes using a shop vac which also cleans the bottom at the same time. Two birds with one stone. My tap water has a PH of 8.5 and a high KH and the only additive is chlorine. I do use a multi-purpose water conditioner when I partially change the water but rarely when I top off.

I've had no fish deaths, other than herons, since my I started my pond in 2003. I also use koi clay if that means anything to this thread:-)

Bailing I am sorry but I do not understand how you came up with only a 6% water change by overflowing the when adding 10% of the volume of the pond. The only way I can see that happening is if there is no mixing of water going on in the pond and the water is added at the surface very near the point where the water overflows out of the pond. First let's assume that there is very good mixing of water going on in the pond. Then as you add water water starts to go out at the same rate that you add. So when you have added the first 1% of the volume it has mixed with the 100% of the pond water and 1% has overflowed of which 1% is fresh water and 99% is old water. Continue this up to the point where 10% has been changed then about 95% old water is out and 5% of new water is lost. Now let's assume there is no mixing of pond water. Then as water is added some water leaves but there is no way to predict weather new or old water is going to leave. But since the water you are adding is probably cooling then the water in the pond it is going to be more dense and will sink to the bottom and not be part of the water that overflowed. But if there is no mixing going on in the pond you probably don't need to do very many water changes as if there are very many fish they are not going to be very healthy in any case.

If all you have in your water that you are adding is chlorine and are adding 5% or less and there is good aeration going on you are usually safe in not adding water conditioner to the water. If you have water lilies in the pond they with remove heavy metals from the pond quickly usually in less then 24 hours.
Mike

Mike that was very informative! Love it when you post and your knowledge is very appreciated.

Regards,
Lisa

Lisa you are too kind. As a professional I have seen or heard all kinds of bad information out there. Some by hobbyist and a lot by other so called professional from all over the country. The problem with information is a lot of times people will accept it as fact without questioning it. Because they accepted as fact they continue to spread it as fact. As good as the internet is it also allows incorrect things to be spread everywhere quickly. I have a very small amount knowledge about ponds and am always learning about them. When I stop learning about ponds I will get out of the profession.
Mike

Every single serious koi hobbiest that I know, without a single exception, do at least a 10% water change per week. Every single one. If it's good enough for them, it's good enough for me. These are people who have a lot of money and time invested in growing their koi to their fullest potential. These are not people who want to keep water lilies in their ponds or other plants. To a serious koi hobbiest, the health and well-being of the animals are the single focus of their pond. And they have been keeping these animals for many, many years this way. The breeders in Japan do frequent large water changes. Why on earth would I want to challange them on this? If the high end hobbiests and the professional breeders do it, I will continue to do it as well. I think they know what is best for the koi.

I change my pond water for 80% at least once every 2 months or when the water gets densed and bit smelly that I can only see the fish when surfacing on feeding time. I use dechlorinated water (10% chemical to 200lt of tap water). Here in South Africa the weather is constantly good but the sun is scorchingly hot in midday. Though I have netting over my pond, floating slimy algae still regularly surface particularly on very hot temperatures and that contributes to the murky appearance of the pond. After 80% water change, the pond looks very good, fishes more happier and active and I can see them way down midway to the bottom (pond 4 feet deep). But take note I got 2 waterfalls on both ends of the pond, one flowing urn on the deepest & one on the shallow part that acts like a strong river stream (that's where fishes love to play-they're like kids proving their might to cross the strong bubbly current). I take emphasis on oxygenating more the pond. I guess maintaining one's pond should suit a personal understanding of its working system. Good observations accounts a lot for its success. Cheers to all pond/fish keepers.

We do daily water exchanges by running the hose into
the pond each day (2,500 gal. pond) for about 12 to 15 minutes (the excess water runs off around the pond) The fish
absolutely love it, as well as the plants surrounding
the pond perimeter...
We usually lay the hose on the bottom
of the pond facing the bottom drain. This accomblishes
two things, fresh water exchanges and also allowing any accumulated waste to flow towards the bottom drain.
We estimate that we exchange about 35% to 40% a week with these daily gradual exchanges each day...
Sometimes we just run the hose full force on the beach section to clean the stones,
the fish love it, and swim in the area and into the hose during the clean up.

Water changes are good for ponds, just ask your fish!
I just want to mention that we don't have to add declor.

Here is a link that might be useful: Beach cleaning video

Hello guys...ai run a pond of about 5 catfish and 3 snake fish(so we call it here cos of the Python designed body)...one of d catfish died and ai noticed a hole in the head...wat could be the cause of DAT...also is there any dangerous effect of changing the whole water in d fish pond once a week or every four days.