If it’s been in the tank a few days it makes no difference to take it out because then most of the fish have already been exposed to ick. Keep the sick fish in because then the ick treatments will help the sick fish and the exposed fish
Honestly, it wouldn't make a difference. The parasite is in the water. If the affected fis does not show signs of improvement soon, then yes. More importantly, when you started treating the water, if you use carbon in the filter did you remove it (the carbon)?
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