my angelfish recently have been getting lot of split fins and the small one looked like it was getting fin rot but super light but i decided to treat with the king british fin rot and fungus control not realising medicines take away the beneficial bacteria too there new tank is almost cycled anyway but there will be a BN pleco in there old tank alone will i have to completely recycle it i have a smaller filter that is cycled and that tank will be just a fry tank soon so should i just get a sponge filter put that in wait for bacteria to grow in that one then move the old filter to the medicated tank