What is causing the brown spots

Can someone tell me exactly what’s going on here? I noticed a few of my fan leaves starting to show brown rust looking spots. Could this be because I added more calmag than normal the last feeding?

What’s the ph of your water and nutrients?

@HornHead I usually keep it between 6-6.5 which has been working just fine. The only thing I did differently was add more Calmag then I normally use in my last feeding

That’s a little low if in soil, while in soil you want it closer to 6.8

@HornHead I never had a problem until now…I rarely take it that low usually in the 6.5 range

Looks as if it could be a calmag or phosphorus deficiency