kyperman said:
I don't mean to give "bad" advice, just trying to be helpful...I would seriously like to know how much water most people do change each time. Maybe I don't need to change as much cause my fish are not real heavy "poopers" and I am running a BIG filter on my 30 gallon. If I had some mongo size fish I can see having to do larger changes more often.
My bigger problem is dealing with my hard well water, but thats another thread. Again, I recently discovered this forum and really enjoy it, so forgive me this.
Well, I wasn't specifically pointing the finger at you, but at a few people -- but since yah asked!!!!!!!!
Most people here do a 25% water change a week, some do 50%. I do 50% sometimes twice a week, depends on the tank and what's in it. My rainbows do better with more frequent water changes, ergo I change the water more frequently.
As for you not needing to change as much -- I'd argue that point big time. Let me explain -- simply -- why routine water changes are necessary:
Once the beneficial bacteria are established in your tank, and assuming it's not interrupted, the "cycle" actually continues:
Fish and other organics produce ammonia. You probably know that.
Ammonia is eaten by a particular bacteria. They produce Nitrites as an end result. You probably know that, too

Nitrites are eaten by another bacteria and nitrates are produced. Again, you are probably aware of that.
Okay, so we have no ammonia and no nitrites. What happens to the nitrates?
Nothing. Nitrates will stay in your tank unless one of two things occur:
1. if you have plants, plants will utilize them. Not all of them, but quite a few
2. you do regular water changes. These will rid your tank of nitrates.
So, even with plants, nitrates can and will build up. They build up much more slowly if the tank is planted, but they still build up. I just helped a lady from Glasgow through OTS, which is what we are really talking about here, in his heavy planted tank. He lost two of his five clown loaches, but we got the nitrates down and everyone is all better now.
Plants can help, but you still have to do your part.
Nitrates are less toxic than ammonia and nitrites, but they are still toxic. Have you ever seen pictures of dead fish floating in a river that has been polluted by fertilizer run-off? The fertilizers increase the amount of nitrates and phosphates in the water to lethal levels.
Nitrates can:
- damage the red blood cells ("brown blood") and thus cause the fish to be deprived of oxygen
- increase susceptibility to disease
- cause a delay in injury healing, thus allow secondary infections to set in
- slowed growth
- sudden death with very little stress (another fish harassing them, catching them)
- lack of energy, stagnant behavior
- new fish usually die very quickly as they cannot deal with the high nitrate levels
Your fish will "acclimate" to the increasing nitrate levels, but new fish cannot deal with such a change. Even the old fish will reach a breaking point and the first ones to go are the bottom feeders.
Nitrate levels in excess of 80ppm are lethal.
Here are a couple of darn good links that probably explains it better than I can:
http://www.thepufferforum.com/articles/small/ots.html
http://www.thepufferforum.com/articles/water/otswater.html
So why'd I type all that? 'Cause trying to explain it to someone else helps me understand it better as well
Hrm, I think I covered anything, but I know if I made an error that someone will correct me.
Roan