Size of tank in gallons or litres.
How many fish and which type.
Water stats in ammonia, nitrite, nitrate, and ph.
Whitespot. The fish will look like they have been sprinkled in salt. Or spots the size of a grain of salt.
Red fins can be due to bad water quality, septicemia.
If you have sensitive fish you only half dose. Need location to name a good whitespot med.
Remove black carbon from filter.
Increase aeration with the high temp and med.