I think that in that case it's due to the PH stress. These last days it was difficult to get the good PH. Always too high although added CO2. So i tried to lower it with acid. BUT i noticed that the PH was always the same, 6.3 - 6.5 before or after acid. My PH meter was dirty, with some algae. I checked the rez PH with reactive drops, it was 4! So now i fixed the water PH and the PH meter and i hope they will recover. In fact they had been in a too low PH for 1 week, do you think it will hurt definitly ?
Fhydro