Just lost a 20 long . Running along nicely , planted , about 18 or so chocolate australe living pretty happily in the tank . but there's a bit of algae starting on the gravel substrate . So I'm in a reputable aquarium shop , that's established a long time , not a Pet*** , one of the few shops I'll buy livestock from , and there's a tank full of ottos . Maybe 50 or so . In a bare tank . They look real good . Ask the guy at the shop " When did these come in?" .... "About a week ago" . So I get a few , take them home , acclimate them and release them into the 20L . Everything's fine for a few days , then one's dead . OK, stuff happens
A day or 2 later , the others are gone , along with one or 2 of the australe . Everything else is clamped up and on the bottom . Got velvet big time . Wiped out the tank within 48 hours .
Oh , well ..... My point is that this kind of thing happens to everyone , despite their best intentions ; all you can do is suck it up and move on .