The tank looks nice, I was wondering who made this panoramic type tank, I'd seen it in another thread. Just a thought that maybe you could raise the light a little to keep emersed growth from getting crispy, you might get some cool flowers or something unexpected.
My DHG was growing but not like I see in other tanks, some have it with seed growing on top, but my Kribensis would pull at it every night and I would net out 4 or 5 nice little rooted plantlets every morning. The DHG lost after 2 or 3 months. I replaced it with Staurogyne sp. 'Porto Velho' and it's doing ok but it's a slow grower.
You should try just double dosing Excel, a 500 ml botlle is $13 and would last you a while, long enough to get your plants growing good. So far it looks good with no CO2 and I really like the rocks and your doing it right with just top off's this is where most run into trouble on a low tech tank with weekly water changes and algae.
With a small tank you can drain your water into a couple of buckets and do a rescape if you don't like it. I use flourite as well with Osmocote gel cap on a high tech tank but I would like to try a MTS tank capped with flourite, I think the plants would do better and we could omit the root tabs, good luck.
Give the shrimp some hiding places with floating plants, etc. but try again with RCS or Amanos.