If the issue is lack of nutrients at the substrate you could try something like nymphoides hydrophylla taiwan, which will send surface leaves up (but is easy to control) for co2 and has a bulb energy store. Other similar species would work well with just additional root tab feeding.
Other crypts should also do well with root feeding as they grow well even in low energy tanks with sand.
I find with my emersed growth that the submerged plants really need heavy feeding to show any growth. The only plants I've found that seem to do ok without any added frets (with emerged growth) is bucephalandra or other slow growers like anubias, java fern etc.