Problems... WTF, over?
I guess it wasn't hot soil after all. The new seedlings went tits up and they didn't have the same soil or any nutes. The older plants are going necrotic. I took the chance of emptying all the cups, dipping the roots in clear water and transplanting into new soil mix. Maybe they will recover enough to continue this grow.
I believe the problem is my Ph corrected water. I used hydrochloric acid, according to instructions on the web; 8 oz acid to the gallon of water. This put the Ph at 6.0. My tested says 6.0, I checked it with a reagent test and it agrees, 6.0. Hopefully I can get back on track with my usual 7.0 well water, which has served well in the past. Then I'll get out to pick up some proper Ph 'down' and try that out. Meanwhile, I've started 10 more Ak-47 seeds in the event that things don't turn around.