Sorry to hear things aren't panning out best, but things should stabilize after this initial period. Just maintain proper ferts, CO2, and photoperiod durations. Partial water changes. Sounds like your trial & error is helping you hone in.
When I DSM'd before, i only tried HC and S. Repens (tropica 049). Never tried downoi until my tank was established. If you want to try that plant again, wait until you're cycled (not that being cycled should affect plant growth, but just to buy more time). You can actually buy "tissue culture" of Pogostemon Helferi from petsmart for a good price.
On a side note, i noticed you're using a magfloat. I find using a MagFox (by Two Little Fishies) works better in nano tanks to get in those tight corners.
Good luck on this build. You'll get it.