You use carrot tops in micro greens? I have never tried that.

too much moisture???

Damping off is pythium, which grows when roots are too hot. Is the heating pad on all the time? You only need the heat for a short time until the seeds sprout. After that point it will encourage pythium, which is basically root rot.

If you get the soil temps down, you're not overwatering, and you still get pythium (I hope you sterilize those cups before re-using), then you might try experimenting with beneficial bacteria.

When I was talking about carrot tops I meant when starting for outside planting. Sorry.

Damping off is always because of lack of air circulation and often too much moisture. Do watering at the beginning of the day and only as much as necessary and provide air circulation however possible. Damping off can occur in even so called "sterile" potting mixes. Steve Gruenke

OK Here is what I do. I grow greens all winter(four years no damp off yet) Micro and up. I start with a potting mix. Use standard ball test for moisture. make a dibbled hole in the center of cell and add vermiculite Depth of hole depends on seed size. With micro greens I spread a layer of vermiculite over the whole surface. Now I plant the seeds and spray with my hand spritzer. cover with clear plastic and put under lights.I do leave the plastic on a lot longer after germanation than recommended, but I have a very dry house due to my heating system. I do not use a heat pad as the lights keep the soil over 70 F. The grow area is at 82 F. while the lights are on and drops back into the 70 F. range when off. Humidity is around 50% One thing I do not water very often when the plants are young, and like you water from the bottom. You can see the moisture on the plastic so no need to worry. So I would ask you what are your soil temps. Beets and carrots like it cool so do most greens. If you are running in the 80F. range germination might suffer. Hope this helps I have had damp off when I first started planting seeds indoors - frustrating. Keep working at it you will fix it

Curt

what about moisture..?