I often wonder if this is what killed my dwarf crays. I had one that lasted a pretty long time, but he was the largest. I think he killed a few, but some died for no apparent reason, including several berried females. I never could detect anything out of sorts in terms of params, unless there's something in our water. Water is a little on the hard side, which should be good for crustaceans.
I also had a TON of pond snails that rapidly had a mass die-off. I've yet to figure that one out, though now I'm noticing a few pond snails and quite a few ramshorn. I haven't added any new plants, so I think the small few I had in my tank simply have favorable conditions to reproduce. But I've not changed anything, other than cutting back on the Excel over the past month.
Deep Blue Professional 50g
Current USA Satellite+ Pro LEDs (24 & 36")
Fluval 406 filter
CO2Art Advance Professional Aquarium CO2 Dual Stage
Hydor Koralia Circ Pump - 425gph x2
DBP 20g long - low tech