that is absolutely not true.. u definitely need a PS. With filter, u can only remove what is undissolved in the tank like fish food etc, but not the dissolved waste..
I'm having a fish only tank but after every couple of days, i have to remove a cupful of liquid waste, almost the color of kopi-o... can u imagine that such stuff are inside the tank?
wat is the size tank u are talking abt? no water changes? not possible. unless u get a denitrator, or have a refugium that has lots of macroalgae to absorb the nitrate, it is almost impossible not to do water changes.
with PS, perhaps u can reduce the # of times u do your water changes. Mind u, the smaller the tank, the lower the tolerance of error, meaning that the margin of error is very thin and any mistake will be escalated very quickly.
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