If the plants are going into a sterile aero system then avoid anything with an organic medium. Here's how I do it: ---get a test tube holder at amazon etc: https://www.amazon.com/dp/B01H6ZR2O8/ref=sxts_bia_sr_1?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=3182441022&pd_rd_wg=eAkLu&pf_rd_r=RVN9GK60NZEAPR7VVCG4&pf_rd_s=desktop-sx-top-slot&pf_rd_t=301&pd_rd_i=B01H6ZR2O8&pd_rd_w=3e37X&pf_rd_i=test+tube+holder&pd_rd_r=CZHYGMH1F80EFVAQG2M1&ie=UTF8&qid=1506170000&sr=1 ---get some thin plastic sheet that can be cut and rolled up into tubes. You can make "cylinders" out of the cut plastic sheet - like test tubes with no bottom. Cut, roll, and place the tubes into the test tube holder. ---stuff a not too dense piece polyethylene fiber (like cotton) into each tube.
---place the seed on top and cover with very light piece of poly fiber or just leave it as is. The plant must get thru the fiber so don't make it too difficult or leave it off entirely. as the plant will be in a sealed environ anyway. ---after seeds are in the tubes place the entire test tube holder into a large zip-loc bag and seal the bag. ---place the zip-loc in appropriate environ for germination (appropriate light and heat levels etc). Poke holes in the zip-loc when necessary. ---harden-off plantlets. ---plants can then be inserted into your grow system and plant holder of choice by simply unrolling each "cylinder" and removing the plant with its roots growing thru the fiber. The synthetic fiber wont mess with your water chemistry and can be placed in net pots etc. Because the fibers are "long" they wont end up in the water unlike some other fibers/mediums. This method works well for me and you can get test tube racks of various diameters. My racks are 16mm diameter and they work for most seeds. As for the plastic cylinders I just bought a roll of PET plastic (type of polyethylene). It's clear and I just cut it into strips about 5" wide. So when I'm done I have a bunch of cylinders in the test tube rack with seeds about one inch or so from the top. Water each cylinder with a lab squeeze bottle and let the whole rack drain before placing back into the zip-loc.

if you use the little 8ml sample size flavors, this is a must have.