Tropical Tony
Fish Crazy
Hi guys. Had my 150l tank for nearly 2 months now and I do water changes twice a week and take between 30-40% out each time. I was just wondering if you can over waterchange tanks?
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I agree with Byron by so glad I didn’t have to type all of that.The quick answer to your question in post #1 is no. You can never really change too much water, provided the tank is biologically stable and the water parameters are reasonably close.
The problem is in tanks where things have not been maintained. For example, if organics increase as will happen if water changes are not regular and substantial, such as when one goes away for a week or two, or if the tank is overstocked (or inappropriately stocked) which means it is not biologically balanced to begin with; insuch cases neglect may cause the pH to lower drastically, to below 7. Ammonia in acidic water is ammonium which is basically harmless to fish. A substantial water change using basic pH (above 7) water will cause the pH in the tank to rise above 7 and the ammonium immediately changes to toxic ammonia, likely killing the fish. But this is the exception, and proper maintenance will not get one into this situation.
Doing two 30-40% changes is good, but if you did one 70-80% change it would be considerably better. The more volume you change the better. For instance, one weekly 70% change is much more effective and beneficial than daily 10% changes, yet the same volume is changed per week. The less water changed at one time, the more pollution is left behind, and it simply keeps increasing.
Fish never get sick from clean water. If one wanted to do a 90% water change every day it would benefit the fish. Discus breeeders do this in their fry tanks, often changing 90-95% not just once but even twice daily. The fish grow faster and are healthier. This applies across the board, provided the parameters are within reason and it is regular. This is the key to a stable biological system. Most of us find once a week adequate, provided it is significant.