Should I Flush and Feed?

Hello, so this seems like a simple problem but being my first grow I just thought I’d check before I do anything too drastic. I grow auto-flowers in coco and currently as I feed them the ppm of the runoff keeps rising (currently about 300-400 over what I’m feeding) and one plant seems to be showing signs of calcium deficiency in flower? (rust spots appearing near the top/sugar leaves). So I’m just curious if I need to flush them first and/or if I need to adjust their food.
It could also be completely normal at this stage. I just don’t want to overreact and do more harm than good. But here’s a not so great picture of the spots if anyone happens to have any insight.

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I use a amended coco and I try to keep my ppms around 1000 in the runoff. You can push it a little higher in flower.

I usually add a 1/4-1/3 dosage when I added nutrients to my solution, which translates to about 400-600ppm.