How much water to change and how often?

[Ken B]

I have seen that some people are doing large water changes weekly on their systems. Some do 50% and more on a weekly basis. That seems like too much water to change every week. I could be wrong and that is why I am asking others their thoughts. The water in the tank develops a balance of micro organisms and these are all in a hopefully symbiotic relationship with each other and the fish. Of course water changes are needed to help cut down nitrates in the water and maybe other things. But it seems to me that doing 50% and larger water changes frequently could keep the water from reaching a nice stable ecological balance. I do see the purpose of doing large water changes to simulate springtime flooding and induce spawning. I normally do about 25% water changes weekly and occasionally do up to 40%. This is on cycled mature tanks. I know also this will depend on your filter system and how heavily stocked the tank is. And I know large water changes might apply if there is something unusual happening in the tank like disease. But why have all that filtration if you have to change most of your water each week? What do you all think? Should I be doing larger water changes?

[ptran]

You pretty much hit it in the head. 10-20% water change weekly should be adequate for lightly loaded aquarium. 40-50% is for heavily loaded and big fish. It is very much depend on the fish load. I know some friends keeping large colony of petro doing 90-100% water change weekly, but they have carbon bottle. The carbon bottle will remove 99-100% impurity in the water and therefore the new water won't adversely affect the fish.

Most of my tank is equipped with "grossly" over-filtration system that I can go 2 weeks and normal feeding without any problem. But I usually do 20-50% water change depend on the tank size and fish load. There is no one-size-fit-all formula, so you have to use your judgement IMO.

[bamzam]

I am pretty new to this so i could be wrong, but I think it also depends on what type of fish you have and their age right? I have a discus tank and everything I've read online (simplydiscus mostly) suggests daily water changes if you want to grow juvies out to 6+ inches

[ptran]

That's is also true for Discus keeper. They do daily water change but I don't know how much. Maybe 5-10%?

[wesleydnunder]

As stated, it is relative to each tank. When Tom Barr first brought about his E.I. method of fert. dosing planted tanks, he suggested a weekly 50% partial water change to "reset" the tank before the following week's dosing.

Grow-out of juvie discus needs frequent( read daily or every other day)large-scale partials of 75% or more. Lightly stocked adult discus tanks can get by with a weekly 50% to 75% partial.

Many aquarists use nitrate as a marker of when and how much partial to do. The reason we use nitrates is that we have tests for it which are accurate enough to give us a good marker of accumulation amounts and periods. Other DOCs (dissolved organic compounds) accumulate as well but we don't have test kits for most of them so we measure the accumulation of nitrate and typically do a partial to dilute nitrate and DOCs. The target amount for nitrates is highly subjective. One aquarist feels they must be kept below 10 ppm while another doses his up to 20 ppm or more to feed his plants.

Lifelong aquarist and contributor to several hobbyist magazines including TFH, Robert T. Ricketts, advocated doing partials frequently enough and of enough volume so that the source water was kept close in parameter to the tank's water. This ensured a plentiful supply of fresh replacement water and in the event that a very large partial was needed in an emergency, The osmolarity of the fish would not be compromised by the large replacement of tankwater with tap that was of sufficiently different chemistry to cause shock.

For me, I keep my tanks lightly stocked, heavily planted and lightly fed. I typically do around a 50% partial a couple times a month. I don't fertilize and haven't tested the water in years.

Mark

[ptran]

The solution to pollution is dilution, and it is literally true in this hobby. We dilute the "polluted" water by doing water change on a regular basis. How much dilution required is depend on how polluted your aquarium is.

For me, most of my bigger tanks are heavily loaded with fish and no plants, so 50% partial is a magic number for me. And I haven't tested my water for a long time too.

[troy tucker]

I use a test kit to make my water change schedule. Ones I have the tank cycled and stocked. I test everyday tel I have a nitrate spike. Then it's time to do the water change. Ones you know about how many day it will take for nitrates to spike. You should know how often to do water changes.
My tanks will spike to 20ppm every 16 days but I do water changes one a week 50%.

[blaciarmd]

water changes can be equated to flushing the toilet. No matter how big of a filter you have and how much chemical media you employ, fish in aquariums are exposed to much higher levels of waste. fifty percent is not big, it should be considered normal. I would only change less if the fish don't tolerate large volume changes.

[morpheus]

lots of good replies here...i agree its really a case by case basis. yes type of filtration, type of fish, size of tank, etc. all factor into your water change schedule. compared to most people on here my filtration is ancient being only HOBs. they are only mechanical filtration, and i do maybe 50% once a week. i mainly keep africans (mbuna) which are much more tolerant than most fish. i do have some geos, and even the tetras i keep are more hardy.

even in my larger tanks, they are not stocked to the gills (no pun intended). so i can go longer than a week if necessary without any impact to the fish.

[Lord Spice]

I have a 210 reef and do weekly 30 gallon water changes