Week 4 DWC update, chasing a calcium deficiency

Running a 4-plant DWC recirculating system in my 4x4 right now, week 4 of veg on some Zkittlez. Plants are sitting at 1.8 EC (roughly 900 ppm on the 500 scale), pH held at 5.9, reservoir temp at 66F. Growth has been solid but i started seeing interveinal chlorosis on the newer growth about 5 days ago, which pointed me toward calcium right away. I bumped my CaliMagic from 5ml/gal to 8ml/gal and brought the EC up to 2.0 EC (1000 ppm) to compensate. pH dropped to 5.7 after the adjustment, so i had to chase that back up. The new growth coming in since the change looks cleaner, but a few of the mid-canopy leaves still show some mottling. Not spreading aggressively, which is a good sign. The complicating factor is my Denver tap water is around 50 ppm baseline with a decent calcium content already, so i was probably underdosing CaliMag thinking the tap would cover it. Lesson noted. I also verified my HPS ballast isn't dumping heat into the res, because elevated temps can lock out calcium even when it's present. Res is consistent at 66F so that's ruled out. Has anyone else dealt with calcium deficiency mid-veg in DWC even with moderate baseline tap water? Curious whether you corrected through the nutrient line or added a separate calcium source entirely. Also open to feedback on whether my 5.9 target is too high for this stage.

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