Never change the filter cuz the old one has all the bacteria that the fish need. You are basically restarting the cycling process... The only safe way (I think) to change filters is to use the old one and the new one at the same time, so the new one gets cycled and then removed.
Yeah that is true. I did test my water with API master kit and my water parameters were good. I still think I have a parasite problem but maybe there could have been a cycle issue. I have started treatment using API's General Cure and haven't lost fish. The bloated danio appears to be reducing in size but maybe its just my wishful thinking.
I will post later if the treatment worked.
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