From your other thread it sounds like your racoon had ich. Ich is not a "really nasty" disease. It can get nasty if it's allowed to: delayed treatment; wrong treatment with snake oils like ich-attack, kick-ich, etc.; foolishly thinking vitamins C plus garlic would help the fish fend off ich indefinitely. Every fish is different; some naturally have stronger immune system and can fight off disease with help of supplements, but some cannot. It's just like some people never get cold but some keep getting it no matter how much supplements they take. the only sure way to not let fish get sick is to get rid of the pathogens themselves.
If your DT is fallow now (meaning no fish at all), then leave it that way for 10 weeks. In the meantime, treat all your fish in a QT with hypo or copper. The methods are posted in the stickies in this forum, so please do read them. Of course, from now on QT all new fish and prophylactically treating them with prazipro and cupramine would prevent this from happening again, most of the time.