Too many water changes?

I feed the fish a mixture of mysis shrimp or bloodworms in the mornng and hikari pellets in the evening. I have the powerhead hidden in the rockwork just to keep water flowing through the rocks. Theres not too much of a current. So id be safe cutting it down to about %20 twice a week?
 
20-30% twice a week is just fine. Gives you a little break too. So that before long you will think you need another tank!!
 
Once or twice a week. Unless there's some other problem or your stocking dictates (discus, breeding tank, etc.), doing water changes more than once a week is just wasting water.
 
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