OK, update. Big water change last night, adult fish transferred to another tank overnight.
Readings in main tank are now:
pH=7.2 (a little high)
Nitrates=0
Nitrites=0.25
Ammonia=0.5
Tanksman, gravel thoroughly washed before it went in, and tank had (just) completed it's cycle...now we start over.
Overnight, we lost our clown loach (stress) and also our harlequin rasbora
(seeking greener pastures, jumped to arid brown carpet)
All remaining fish back in main tank now. First stop today, lfs: more Cycle (running low now!!! ) and some ammo-lok.
Once again, a huge THANKS for your help through this.
(Plus, we are selling our home, agents through in bulk today) :-?