How often do you change your water?

30% once a week..
 
20 % weekly. Two consecutive 50 % every 3 months.
 
I do 30% weekly, and once a month I do 30% 3 consecutive days.
The Lightly planted tank I monitor and do what it takes to keep the nitrates below 20 PPM at their highest point, the heavy plant tank, just get 30-40% a week. Nitrates stay below 5 in it without a water change so the testing doesn't help me much.
 
30% water change every Sunday whether I want to do it or not:p 50% on the last Sunday of the month. I keep a journal of what I do to my tank in the event that I do something that whacks my tank out.
 
I do 30-33% changes on each tank weekly, except for one of my 20's that has Keyholes in it. They HATE water changes so they only get a 20%. My Africans, I try to get twice a week because they are overstocked to cut down on aggression.
 
Each of my aquariums get a minimum of 2 20 - 40% water changes weekly. And occasionally, similar to what richer does, I will do 2 or 3 30 - 40ish% water changes in a row.
 
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