Middle leaves yellowing

What is the soil (sand?). What are you feeding?

Soil is topsoil w/rice hulls, the half-inch layer of sand on top was to get rid of fungus gnats. I use general organics “grow” in distilled water, plus hydro guard, pH’d to 6.5. Also added zinc a couple weeks ago but no change.

When was the fungus gnat problem? How bad was it? Maybe they damaged the roots? I've never grown in top-soil. It seems like that might be heavy/dense, slow-drying. With it being covered in sand, can't see what it looks like.

It was pretty bad, they finally cleared up about a week ago. Had root rot before that, hence the switch to fabric pots and a true wet/dry watering cycle. Hydroguard too. There were definitely some twisted/stunted branches from the root rot, which i cut off, but this yellowing issue is fairly new.