I had soil earlier this year, transplanted to hydrotron. Also, used a peat based seed starting mix for everything going now due to frustrations with rockwool.
The damage pattern is/(was hopefully) essentially identical to that of thrips, though I never identified single one on this run. Earlier this year I saw white clusters of them and black spots (their poop from what I know) this was during my transition to hydroton. In addition I had springtails in the flood and drain ealier this year, hasn't been a real good grow year for me lol.