12-08-2006, 03:52 PM
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I do a 50%+ water change each week. Sometimes my fish don't mind, other times they pout for a day or so.
Here are some key factors when you do a water change:
Know your GH and to a less extent, your KH. Large swings in either one can cause stress to the fish until they acclimate again. When I do my water changes, I immediately do my macro dosing to try and keep the GH and KH swings as short as possible and as little as possible. I also add my dechlorinator immediately after the water change. If you want to, you can add the dechlor, MgSO4 and your Calcium to the water if you are using buckets.
Another key is temperature. My fish almost revolt against me when the temperature is higher than the water in the tank. I always shoot for about 2 dergees below tank temperature for my water changes.
One other thing is you are changing a little too much if you are doing 75% of the water. Unless you balance your KH and GH, the swings in both can be very stressful.
You may also be seeing a large swing in your pH. Test your tank and test your tap water after you leave the tap water out for 24 hours. This will allow the CO2 to gas out and give you a more accurate reading. If the swing in pH is too large and your KH is below 3 dKH, (~48ppm I think) then your fish will stress and it can be very harmful to them.
Do you inject CO2 for plants?
Is the test kit you are using a liquid regent or test strips?
A lot of things can cause stress at a water change but we need to know what your KH, GH, pH of tank and tap water and anything you dose as far as ferts, what type of dechlorinator and anything else you add to really help you properly.