Topz,
My growbed is hydroton approx 70 gallons? It is the IBC top flipped over 10" deep. Only 5 gal makeup water added. There are 9 feeder goldfish getting big 2-4", 3 channel catfish 5-6", 5 hybrid bluegill 3-4", 6 yellow perch 3-4"...=23. I expected the feeder gf to be eaten but they grew fast.
I am using chiclid feed pellets because they float and some goldfish flakes because I am taining all for high quality pellets I got from the fishery the sold me the cats, bgs and perch. There have been no fatalities these past two days and ph has dropped to 8.1 from 8.7 in three days on its own. My FT has quarter size river rock and plastic fernery and some pvc refuges.
No other additives, when I pulled the pump and tubing to clean, I just used the jet setting on a standard hose nozzle...no soaps etc. The 800 gph pump is working like it should now, flood/drain every 12-15 minutes, diverter valve wide open, spilling/aerating back into ft.
The night before the dieoff began, I heard a louder than usual thump against the tank wall as feeding subsided. The wild ones are very aggressive swimmers at chow time. Banging into the walls is common. But this time was different. It may have been the bluegill that died within hours from head trauma.