when you det any disease you have to look at why your fish got sick in the 1st place, eg check temp, ph, ammonia , have you put knew fish in?
have the fish been stressed, new fish food, sprays, anything new put in the tank.
with white spot it is common at this time of year because of the cold weather, turning your temp up does help stop getting it also not doing big water changes.
but because you have it turn your temp up to 28
remove carbon if you us it (i do not like carbon so i would use it unless you really have to)
i would have use white spot cure , tonic is not a good thing to use and i dont think it should be sold but thats just how i feel haha
turn your light off as much as you can as that does help with white spot oh and also if your fish are sick they dont eat as much so cut down the feed.