Brown Patches on Older Leaves

Definitely calcium deficiency bro. I had the same then after correcting with some nutes the newer foliage came out fine. I’d keep an eye on the newer leaves.

Hello It looks like the speckled look from a calcium deficiency and with the one leaf showing it dominantly on a lower leaf at the tip where the light hits it is decent indication. I think every plant varies on how calmag hungry they are, so possibly just increase the amount for the one plant having the spots. You could try to let the ph go through the 6.2-6.5 range not always at just 6.2 and then maybe raise to 1 tsp per gallon and see if it stops spreading. I think the plant still has awhile to go so its definitely worth solving the problem.