Mold at 3 weeks - advice needed

Hi all,
Thanks for reading. First time grower trying to get through my first harvest. This is the second time I've had mold at the 2 mark. Can anyone offer advice? I got pics of the stem and set up. It's about 75 - 80F and mostly 30% humidity. I have covers over the holes not being used but some light is getting in. Would a HEPA filter help before I have to use the carbon for the smell? Also I have a 1.5g reservoir for 1 plant and have the water 1/3 - 1/2 way up the net pot. Am I over watering and would that be causing the mold?

Thanks!

Use a large osc fan 24/7( all plants moving) and that will reduce this mildew problem you have.

Fill the water in the DWC to about a 1/4 inch under the net pot. You want the roots to sit in the well, not the pot. Otherwise the medium will always be soaked. Feed the plants with tubes from the top to allow the water to run through and drain.