I got too confident. I had a good system in place, and one day I didn't follow it. I cut 8 nems, 4 each from 2 strains, and just tossed them back in the baskets without keeping them isolated with extra carbon first. I think that started the tail spin. I don't think the bio pellet reactor, GAC, and skimmer was enough to deal with all generated waste. Since adding a sump with live rock, the nems stopped getting excessive foot slime, algae on the baskets stopped growing (I was cleaning the baskets weekly, now I do it once a month) and the surviving nems stopped turning to mush!
I just did my first cut in months tonight. One nem only. I'm leaving the cuts in an isolation tank for 24 hrs.
Fingers crossed.