It's been many years since I've done this stuff but the basics haven't changed much. Beyond standard nutrients adding auxins to your media will greatly stimulate root growth. Kinetin/cytokinins will stimulate more vegetative growth but roots usually are more what you want for propagation purposes. Also for more root growth typically you'd want to go with a softer agar say 1/2-1/4 normal. As you note, the specifics need to be worked out for particular plants but using phytohormones as above will let you better tailor the growth. Plate up a range of concentrations to see what works best and then go from there to better optimize.Lack of rooting is why ive been tweaking my own rooting media to find out how low I have to cut nutrients. And gotta make sure you don't use too much agar. Most of them do not like media that's nearly as solid. I've had E. parvula (dwarf hair grass) refuse to grow runners, and only grow roots between agar and container walls because agar was too firm. Hah. Darn things. Picky AF. I thought I'd just transfer techniques from terrestrial and run with it. Nope. Gotta optimize each phase of media for each plant. Far more work starting up than I anticipated haha. I love it though
I've not tried to use them for aquarium plants but there are off-the-shelf rooting compounds that you can get easily if you don't have access to lab grade products which should work well for DSM use, e.g., https://www.amazon.com/Miracle-Gro-...=UTF8&qid=1540367419&sr=1-1&keywords=fastroot