water changes

I think its something like 20% every 2 weeks.

i have a 4' tank and i change aprox 10gallons a week
i think it just depends on what fish you own and the size of your tank, if you could post what you have it may help?

I have seen many different views on water changes. I've seen people do them once every 6months, 1 a month, every week, 2 a month, etc. I used to believe if it isnt broke dont fix it. But that was the old me. Now I will do them once a month if not 2 times a month. In the winter time I only do them 1 time a month because I'm loosing 28gallons every 2 weeks at least, when the weather strats to warm up and evaporation calms down I will start back on 2-3 times a month.

I do 15g in a 75g every 2 weeks.

How much water and how often will i need to change it in my 20 gallon tank with 10 gallon sump?