I bought new fish not long ago and didn't QT them, all that was in the tank was my pleco (I had to euthanize my betta so pleco was alone). Fish turned out to be sick-I'm still not sure what caused it. One guppy died over night with no visible warnings-all I could think of is it looked a little fat compared to the other two but I figured it was just more mature and therefore bigger. About a week later, one of my habrosus cories was dead in the morning, only vague "symptom" was his barbels seemed a little shorter the day before but was still active and eating etc. The cory seemed to have popeye but I thought maybe that happened after it died, maybe not. A week later another cory started acting sick and died a week after I noticed that, so two weeks between the two deaths. The last cory showed the most symptoms-rapid breathing and being inactive, eventually lost all color except for the black markings, developed pop eye, would curve sideways (into a c-shape if looking from above) and right at the end seemed a little bloated-his mouth was stuck open. He'd also slightly spaz and swim erratically for a few seconds before resting again.

I think I might be dealing with TB in my tank but I can't be positive, it also sounds like it could be NTD? Or even columnaris?

I treated with Maracyn 2 and fed antibiotic food, and also used Jungle Labs Parasite clear after because I noticed what might or might not have been an anchor worm on one of the guppies, and were flashing.

It's been a week and a half since the last fish died and I'm watching them all like a hawk. So far everyone seems to be okay though, the cories aren't as active but I'm pretty sure it's just because there's only two left.

How long would you wait before feeling okay with buying more fish? I think I'd like to wait a total of 4 weeks since the last death but I'm still uneasy about it all. And I'd certainly be QTing new fish for a couple weeks.

(and figured I'd say-my ammonia and nitrite are zero, nitrate around 5-10 ppm [the API colors look the same to me lol]).