What is this?

Got new problems emerging with my plant on day 23 of flowering. Can't figure this one out. What do ya think this is?

Maybe too much light or pests.

Is it just on the bottom leaves?

I suspect your nutes are off a touch and your plant is robbing from the bottom leaves. Details on medium and feeding info would be helpful.

Did you blast it with a pk boost? It looks like a k and mg and problem maybe?.... I hate deficiencies. They're so confusing.

Calcium Deficiency calcium deficiencies tend to show up in newer growth (upper leaves) and middle vegetative growth.

Is it starting at the top or bottom of the plant?

If im seeing correctly it looks like Black spot disease by looking at the leaf picture. If that's the case then you need to pull all the leaves with it off the plant so it doesn't spread. Before you go ripping off your leaves though go look it up or take a picture of the whole plant the same way you did with the leaf. Pics with HPS on suck.

need grow details... are you a nail biter?

It's in a base soil of happy frog smart naturals with super soil in the bottom half of the pot. I thought it was a ph problem and I checked my runoff ph and it's at 6.5. It's in the lower and middle part of the plant. I'm thinking it's a calcium deficiency though because my tap water is coming out at 56 ppm and I thought that would supplement calcium but from the looks of it, it's not cutting it. I sure hope this isn't a disease lol