Friend has the exact same issue...rust spots that looks like ph spotting but have lowered PH all the way down to 5.2 ......everything check out....

How many plants do you have attached to the 15 gallon res?

I have tried everything I know to help him.....
jbarth22 Reviewed by jbarth22 on . PH dropping I've just come off fixing my ph from swinging WAY too high in a short time (it was not normal ph drift). I replaced the water and flushed, things seemed good until a few days later. Now my ph is slowly drifting down from 6 to 5.5 in the course of half a day. The plants are getting worse. It started out as ph spotting, but grew into mg, cal, or phosphorus deficiency (I strongly believe it is the mg that is locked out and they are also a little K deficient in parts, yellowing has occured as Rating: 5