p/k deficiency

Hey y’all! This grow has been going great up until this point. I’ve noticed some shit spots or like bruises on the leaves, as well as some rust spots (like calcium deficiency) on my ATF plant. 4x4 Tent 480w Meijiu board (3500k) Ffof/happy frog (50/50) with 3 parts perlite, 1 part EWC. Water with...

At first I thought it was a cal def until I saw some newer growth with these brown spots also on mid and bottom fan leaves. As im doing more research on the blotches I see it could be p/k def or a rust burn? Its only on one plant and It first started to appear after a 2nd foliar feed with MgSO4...