Originally Posted by Godmadefish
Yeah, I asked about the water changing because I've always been told that if you take out too much, you take out all of the good bacteria that the fish need. Other than when problems come up with the tank, how true is this really? Just wondered; working at petsmart I've been told it should be about a 10% water change weekly, and about 20% one of the weeks of the month. I thought it had something to do with having less space with the ammonia and such that they put off as opposed to the way it is in nature. Not contradicting at all, I just want to make sure I have the right info. I know personally that petsmart does Not always give all of the information 100% for pets, which is why I have to learn on my own most of what I know, and there's always more to learn(after all God made alot
of neat creatures!). Thanks for all of the feedback, because besides helping me with my own tank, I get to learn something new, and I can also use that to help people with their own fishy problems.
Asking questions on here is not a problem for any of us, believe me. None of us will learn if we don't question.
Water changes are somewhat determined by the aquarium, by which I am referring to the number and type of fish (different fish have a different effect on the system) in relation to the water volume, and whether or not there are live plants and how many. Fish release chemicals (pheromones and others)that send messages to other fish, either their own species (characins are now known to be highly adapted at this, sort of communicating chemically) or warning others; and many botanists believe plants do something of the same (called allelopathy). These various chemicals and pheromones will build up in the water un-naturally in an aquarium; in nature they would be carried away. Plus there is the build up of ammonia, and nitrates too especially in the absence of plants. None of this is "natural" to the fish.
In nature fish are never in the same water for more than a second. The only way to come close to this in an aquarium is with a water change. Breeders of discus frequently change 90% of the water several times each day, and the fish grow faster, stronger and are healthier as a result. So changing more water more often is reducing all this "stuff" that the fish find irritating and stressful, which leads to health issues.
As for removing good bacteria, all the good bacteria in an aquarium colonize surfaces, not water, and most live in the substrate. Not just the nitrifying bacteria nitrosomonas and nitrospira, but the aerobic (and anaerobic) bacteria that are responsible for breaking down organics into nutrients for the plants.
We have had a few threads on this forum lately about all this; I usually refer people to the 2 articles in the November and December 2009 issues of TFH on water changes for more information. The author goes into many of the reasons why significant water changes performed regularly are essential for a healthy aquarium.
The only time a large water change could be detrimental is when the parameters between the tank water and the added water are significantly different, such as might be the case when the aquarium has gone without regular water changes and the pH has dropped. This can cause the pH to shift from acid to basic with the water change, and the ammonium in the acidic water becomes ammonia in basic. In this case there are two problems for the fish; the ammonia, and the sudden pH shift which is stressful if not worse. But in a well maintained aquarium with a steady balance biologically, the larger and more frequent water changes will assist in keeping that steady biological equilibrium.