Sudden yellow sploches. Help!

I had what seemed like overly strong nutes last week whenI was running about 740ppm (.5ec scale) so I diluted the solution a bit to 500 last weekend and let it further dilute down to 380 by just topping with water. Last night, I added back flower nutes to about 650ppm over the course of two 1-gal refills spaces about 10 hrs apart, but it's back at ~580 now. Not sure if my reading last night was from nutes that weren't fully mixed yet. Now, I see these yellow splotches and not sure what it is. (leaf in center of the pic).

This is happening to about a handful of the larger fan leaves in the upper 1/3 of the canopy. Young leaves at the top are growing fine so I don't think it's light burn. Older leaves at the bottom are fine as well. The other leaves with some spots are from a prior cal deficieny (I think), which was fixed when I added CalMag.

RDWC waterfall in sterile res
Mars ts1000 light at 100%
2 plants, 10gal total
68F res temp, 78 grow temp, 52rh
5.9 pH
Using GH Flora at 1/0.5/1.5 mgb ratio with CalMag Plus at 0.75tsp/gal.
Roots are nice and clean, no funky smell from rootzone, res smells the same as it did a month ago, no issues there afaik.

I was adding H2O2 before but just switched to a bit of chlorine since I’ll be gone all weekend. Leaving in 5 hrs. Is the added chlorine causing this? I used the same amount before and no issues.
 

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