can you really do to much waterchanges?
 

just wondering if there is such a thing as "2 many waterchanges" remember my system is only 18 gallons or so, and i'm skimmerless,

right now i'm doing 5 gallon water changes every 7 days or so

Absolutely.you could do a 50% change if you had a dangerous water condition or disease,but to do more than regular water changes could cause an imbalance in your system. Even cleaning your filtration too much can have an adverse effect. One of my tanks is a 2.5 gallon .I thought I would be a good custodian and change 50% of my ceramic doughnuts and wash
the sponge ,well hello algae! It is also too much stress on the inhabitants.

you can change as much water as you like, 25% every week is fine and not going to hurt anything, I would even go as far to say that you could do 10 gal a week and be fine.

Steve

In other words if you change out too much water, too fast, you will kill the nitrifying bacteria

how would you do that nitrifying bacteria don't live in the water column they live on the glass, rocks etc.

In my 12g and 24g Nano's I change at least 50% of the water weekly - sometimes up to 75%. I don't skim these tanks and feel I need to do this for water quality. I also have sponges in these tanks which tend to be nitrate factories so they get well rinsed at the same time. As has been said your bacteria live on surfaces and not in the water column. I just make sure that my temperature, PH, and salinity are all the same for the change water as the water in my tank .