Aquarium Changing Confusion?

Generally, what I've always heard is about 20% weekly. Changing only 10% every month is probably a bad idea, unless you have a really understocked tank with lots of plants and a good filter. I do a 20% water change on our 10 gallon every week, and for the smaller aquariums (the 5.5 and 2.5) I do about a 50% weekly, but that's only because they're so small to start with.

As for not allowing the biologicals to set up, most of the nitrifying bacteria live in the gravel, on the plants, and in the filter. Relatively speaking, very few are living in the water. Since you've not had any trouble with 50% changes weekly, it probably wouldn't hurt to continue them, but really only 20% is recommended, except for small aquariums which doesn't really apply to your situation anyway!

Sounds like your doing fine, especially with the 10g. I own 10 tanks and do 50% weekly in every one except my SW tank. My tanks range from 10g to 125g and all are severly overfiltered(12x plus water turn over an hour).In my 10g fry tanks, I sometimes do 2- 50% h2o a week. Your biological bacteria is in/on everything in the tank(substrate/deco/glass/filter), but not the water. Water is still cheap nowadays and PRIME as a declorinator goes a long way, so why not give them fresh water? Not every pet store person knows there stuff. I say keep doing what your doing, I do the same, and people are amazed at how clean my tanks are when they find out some have been running for over 5 years. You go girlfriend and make sure the hubby helps, your only doing 20g a week, I'm up to about 330g a week change and noone is gonna convince me otherwise. BTW once your tank has been running for 6 months or so, I would suggest saving the money for test kits. I only test for NitrAtes(aquarium pharmacuticals liquid kit), and usually only 1 every 2 months or so. Now if I could only get the wife to help =(.

OK 50% a week is a little excessive. Usually I change 10 to 20% and I use a gravel vacuum to remove the water(2 jobs at the same time).

The biological filter is not in the water, so much as built up on surfaces so doing such large water changes isn't going to really harm it just deplete it for a few days.

I use a small sponge filter hidden in the tank and NEVER cleaned, just "squished" out in the tank water to remove the goo, to keep my bio filter in top shape.

20% every other week. If you look at old books from the 1960's and prior (back to 19th century), they rarely mention water changes at all, yet fish didn't die. The reason, something called a "balanced aquarium" something nearly impossible to achieve was the theory. Can it be done? Yes. Water changes and other modern fishkeeping methods are more practical however.

I hold with the majority here. You should change 25-30% once a week for most typical tank sizes and set ups, cleaning from the gravel as you go. As far as your advice to change what you are doing remember the old addage "If it ain't broke, don't fix it".

MM