Okay, in the past, I've had a 10 gallons tank and I did 25% water change every few months. When the water goes down, I just simply add water to the tank. I never have any problem with all my fishes for 3 years. Now, I have a 30 gallons tank and I have some questions. I've read that water change is a must every week at 10% or every month at 25%. I do not believe in the weekly change, but a monthly change sounds fine. I recently learned that each time a water is added to the tank, there are more minimals buildup. Is this true? Wasnt the treatments suppose to zap all the minimals away? Should I use distilled or spring water from the store instead of the tap water? The water in my 30 gallons tank is great at 7.0 PH with no ammonia, nitrate, and nitrite. There are currently 1 tablespoon of salt per 5 gallons = 6 tablespoons. I am curious on what is the best water for the fishes.