If the tank is currently at 30*c and is not fluctuating, You don't need another heater. I would get just a small thermometer like this one:
https://www.amazon.com/Marina-Float...02114841&sr=8-3&keywords=thermometer+aquarium
to see if your temp is correct.
Duanes gave you good advice with the salt and heat, I would advise you follow what he said and it should get better but may take more than a week or two, and your other fish may start to show spots before the ich dies off. Just be patient
https://www.amazon.com/Marina-Float...02114841&sr=8-3&keywords=thermometer+aquarium
to see if your temp is correct.
Duanes gave you good advice with the salt and heat, I would advise you follow what he said and it should get better but may take more than a week or two, and your other fish may start to show spots before the ich dies off. Just be patient