At the moment I am testing a number of substrates for hydroponic grows in trays: pvc screen, tule mesh, paper towels and none. At the moment I think that paper towels for brocolli and no substrate for sunflower may be the way to go. If I have to, I will go back to coir.
I have a lot of other variables to work through to find out what the seedlings like and what produces the best yields.
I have tried no nutrients (straight water) and mild nutrient solution and the results are better with nutrients. For 10 day sunflowers, I get about 2x the seed weight yield with only water, and 4x to 5x seed weight yield with 25% of full strength nutrient solution (2g NPK, 2g Calcium Nitrate, 1g Magnesium Sulfate in 4 gallons). So a clear winner there.
One issue is that on day 3 there is a strong odor - urine or aquarium smell. It is quite strong. It seems to go away by day 5. I suspect it is coming from decaying seed hulls but ???. My temperatures may be too high. I am using trays which hold puddles of water/nutrient solution. I am using them because they were cheap and easy to find. I would prefer to use a flood and drain tray with a sump that fully drains the tray. But I will see if I can make what I have work.
I am in the middle of trials and they don’t always work out well, it is a matter of testing the edges to find the ideal method. So I am not filming my current trials. But when I get my system dialed in, I will start posting videos with recommendations on how to successfully grow microgreens in the system.