W/C's and drop in SG

[michika]

It sounds like you need to pick a set point of specific gravity for your tank, and then read up on how best to maintain it. I'm not sure if your confused between topping off, and water changes, or if you just don't understand them out right.

Watch this ---> http://www.youtube.com/watch?v=kSTY346rros

In short, if your confused please ask. Many of us here are more the willing to help you out and get you pointed in the right direction.