Please help sick discus

hi there, three of my discus felt sick their body have turned dark and fins closed and now tail starts to rot. Ammonia, PH etc are normal. I suspect it was due to temperature fluctuation. My heater malfunctioned and i didn't realise the tank water has dropped to 24 C for a few days. Other discus remain healthy except these three. I went to local aquarium they gave me some powder which is used to de-worm but on the bottle it also says to use when discus turn dark and rubbing against object. Have used this medicine for 3 days now and did a 50% water change and added more medicine to keep consistency of drugs It does not seem to help and in fact tail rotten started today.

could someone please advise what medicine do i need to get and what other things i have to do in order to save these discus?

sounds like PH burn

you need to ensure your GH is stable . Utilise your KH powder to do so.

deworming medication will not fix fin rot. id stop using whatever they sold you.

ensure your tank temp is 30, utilise rock salt, turn off tank lights and ensure adequate airation.

good luck

Temperature shock can weaken the immune system of discus, so I'd suggest you raise the temperature to 32 degrees and hold it there for at least a week.

Do several large water changes to remove the medication then add rock salt or cooking salt at the rate of 1 heap teaspoon per 40 litres of water.

Do a 50% water change every day, adding salt to the new water to maintain the level of 1 heap teaspoon per 40 litres.

You should see an improvement within a few days.

HTH