FINWIN
This particular system is around 1000 gal - two 240 gal tanks and a 500 gal sump. Old soaked/washed concrete is benign in a large water system with 100% water change in 3-5 days 24/7/365 I think. In a small tank, it could be a different story.
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One time is a fluke, two is a pattern. We lost Floyd the same way as Bruce, except Floyd lasted about 10 months versus a couple for Bruce. Same symptoms of heavy swelling over the entire body points to the same pathogen, perhaps the same old columnaris introduced into our tanks in 2018. Three year old, 1ft Floyd: