Originally Posted by Pogthefish
bettas r not germaphobes like humans id stick to 30% weekly 50% will be bad for a cycle and its only 2 bettas, they can handle it
The 50% doesn't harm the cycle. It just slows it do to the fact that there are living creatures in there, and you don't want things like nitrites building up very high. Replacing the filter cartridge messes up the cycle. Changing the water will have no effect, the fish are constantly feeding the cycle themselves, you have to avoid something like a nitrite spike during fish in cycling.
Like I said 30% weekly is fine for them after the cycle.