Well, made a big mistake–not thinking and not acting by testing water for nitrates. I lost one CPD and then another but never found them, figured the shrimpies ate them. Last CPD was constantly swimming back and forth in same pattern before it disappeared.Then an oto died and I couldn't find the other, figuring same thing happened. That finally set off alarm in my thick skull and I tested and got reading of 100 so did 66% water change and with no fish left in tank am letting it run with only shrimp and plants. Will test again before I put any fish back in. Hope I've learned a good lesson: change water regularly and when fish die–there's usually a reason and dead fish can really affect water quality, even if you think shrimp ate them.