slits in my fishes fins

Question
i would like to know how to solve my on going fish problems. i would like to know how i  can Treat my fishs  that all seem to have slits and dents in their fins? thankyou
i have 9 fish in my tank it is 65 litres. the fish look ill they are moping about and have slits in their fins. i feed them nutrafin max flakes or frozen bloodworm. they seem to be swimming the same.they are not agressive towards the other fish. i do a water change every 4weeks i put aquaplus and conditioner into the water when i do a waterchange. my water temp is about 24degrees c.i have a filter that i clean out every 5 weeks they all seem to be eating ok. i have 4 cloud mountains 2 platys 2 angel fish and 1 catfish. how do i solve their slit fins and mopey looks?

Answer
Rebecca,

 You are border lining over crowdedness. Water changes need to be done every week removing 25% of the water each time. Sounds like your fish are suffering from fin rot. This is caused by bad water quality. It is very important that you are testing the water weekly as well. You can get a wide spectrum medication to treat the fin rot. Make sure you follow the directions on the medicine bottle. Once you start changing the water weekly and use the medication you should start to see a change. Start treatment right away to ensure the fins do not rot off completely. If this happens, you might start losing fish and the ones that do not die will not grow back the fins. If after treatment of 7 days does not help the problem, or things get worse let me know.