i am getting kinda frustrated with this tank. when i first introduced fish to it they all started scratching against rocks. so i treated it for parasites that might have been making them itch. they went a few days and then started itching again. so i treated them longer. i have been using the malachite green by kordon. both times i cleaned the filter media with very hot water. and i did all the water changes as per the bottle of meds. last night i put the filter media back in and went to sleep, they had stopped the itching for about a day and a half. this morning they were itching again!!!! and all my water levels are good, the ph and so forth. don't know what to do!!