After removing CO2 and lowering temps (switching to external air) - plants sick?

[SamandMax]

Is AISI-302 stainless steel good for the reservoir with nutrients?

In order of operation, I always double-check PH. Then if PH is good I refresh the nutrient solution. Your problem there looks to me like a P def, which is rare and suggests either incorrect PH or contamination. It could also be magnesium which is also likely if you have an RO system. Both would be fixed by fresh nutes and correct PH. Check your PH, if it is over 6 it could be the cause of a P def, if it is under 5.8 that could be the cause of a Mg def. If that does not fix the problem then you…

Am I correct and the potassium range for hydro is entirely different in that post?