My son's fish have what I am told is fish rot on the tail or a fungus (tan/brown looking like it is decay?). ?

Question

The clerk at the store said to use tablet medicine for the fish and to remove the active carbon which I did. It changes the water pale green in color, but the fish don't seem to be bothered by it. How long should I go before doing a 20% water change and starting to get the medicine out of the water?

Answer 1

What you really must do, is stop spending money on fish to get them well. Flush them and buy some more!

Answer 2

Since every type / brand of medicine is different, the instructions should tell you how long to treat the tank.  Doing a routine 25% water change and add the carbon back in the tank.  The carbon will pull the meds out of the tank for you. Just follow the instructions as to how long to treat.