Water Change Percentages

Soulmanure

Soulmanure

Soulmanure
Jan 27, 2005
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0
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54
San Francisco
So after having read a number of posts on the site about water changes, my sense was that somewhere between 30 and 70 percent weekly was a good range for water changes.

Well, I went to my LFS, which is run by a pretty knowledgeable guy (he's had his store for 20 odd years) who has a lot of great tanks and does a lot of his own breeding, and he was astounded by that percentage. According to him you shouldn't do more than 5 to 10 percent a week because the PH alterations are too extreme. He said, and I've heard this phrase before, that this leads the fish face to face, or pucker to pucker, with the "Silent Killer," the PH swing.

So now I'm wondering--which story do I believe?

By the way, his fish are always beautiful and healthy.
 
Cleaner water meand healtier fish. Constant/large water changes ensure cleaner water.

When you have a tank that has been running for some time, the water chemiostry should be close to your source (well/tap) water. When you remove old water and add water of the same chemistry (Ph, hardness, etc...), ther should be not a drastic change in the total tank chemistry. About temperature, if you do things right, you will et water reach room temp before adding it or even you'll have useda heater to make it the same temp you normally keep in your tank.

Sometimes, it's necesary to modify normal tap watewr condition to meet certain requirements needed for some delicate species or to trigger spawning behaviour. This is normally left to the most experiienced aquarists, and they will also modify the water before they do their water change.

So, if you are doing things rigth, and you care enough to know and uindesrtand a little water chemistry, you'll undesrtand that even a 100% water change should not mean a drastic change in fish living condition. In the other hand, if you just put a hose right into the tank, and let the tap water fill it without previous check of temp or conditions, you should stick to smaller water changes to prevent the damage you'd be doing to the tank's stability.
 
Whatever you do, DON'T believe him.

If you want to experiment with it, start doing 5% water changes for a few weeks and monitor your nitrates and see what happens. See if they reach a stable and safe level or if they go through the roof.

I think you'll find that "Old Tank Syndrome" is the real silent killer.

I do 50% water changes every 4-5 days and my fish, especially my very sensitive fish, are incredibly healthy and happy.
 
No Swing

Changing 30 to 70 percent of water a week is not going to cause pH swings. Because the water will be more stable with the addition of new alkalinity. pH won't change significantly in a week with large water changes. So there won't be any swing.

Perhaps you misunderstood the LFS guy. Not performing water changes for several weeks and then suddenly performing a big water change will cause a pH swing. Maybe that's what he meant.
 
often people who have kept fish for a long time are behind the times as far as water changes go.

mostly because it used to be thought that new water killed because water changes were done so infrequently that the fish had adapted to increadably high nitrates and when water was changed in larger percentages the major water chemistry change shocked the fish to death.

frequent large water changes prevent the build up of nitrates and you will find that your fish get sick less, breed more, and have much more vibrant colors than if you stuck to your LFS's suggestion. In all likelyhood he is a great source of knowledge in other areas but he's an aquarist of antiquity if you will and you can ignore his water change suggestions.

I promise your fish will be far healthier if you do the large and frequent water changes!
 
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As I suspected--I figured that the larger changes would be fine, but the LFS guy has great fish and seems to do fine as well. He also seems rather meticulous, so I didn't want to discount him immediately.

Thanks for all of the info--I think I'll stick to my weekly 40-50 percent changes.
 
Just venturing a guess, but he is probably assuming that the tank will be kept at a different ph than your tap water or whatever water source you are using. I'm fairly certain that most of us are using tap water and not chemically altering our ph. I just have to think that if you had an african tank sitting with a ph of like 8.3 or so and had tap water of a ph in the 6.8 area then that might be a bit of a shock to the fish. I don't think it would kill them though since I believe in general rain water wouldn't be the same ph as the water its falling and running into.
 
If you are working with modified water, there are certain proceedural changes needed IMHO & IME. You need to do the water mods before the water is added to the tank, so either one bucket at a time or in a separate, circulated and tempered container, then add the modified water to the tank by pouring or pumping. Do not add unmodified water to the tank and then do the mods in the tank with the fish - that is doubly stressing the fish.

If you are not doing water mods, and if you partial significant percentages frequently, there will be very little change in the water parameters between changes unless your tank is grossly overstocked and overfed. If the later is the case, you need to increase the volume and frequency of the partials to compensate.

The healthiest, cleanest tanks I have ever run had (automated) daily water changes. Many breeders of tropicals do massive (>100%) daily partials, Guess what? That is alot like, if still less than, what the fish experience in the wild.

RA - Thanks for posting the water change links.
 
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