I've been growing parva emerged for a couple of years now.
My favorite mix, and I grow most of my Crypts in pots, is just simple large grained, sterile sand, the play or filter type and decomposed peat 50/50.
Matter of fact, this is by a wide margin the most sucessful mix I've used for any and all emerged aquatic plants, and I've got a bunch too: Urospathas, Crytospermas, various Anubias species, Lasiomorpha senegalensis, Lasia spinosa, Homamenia sp. Laganandra sp. plus the Crypts and some other stuff nobody has ID'd yet.
Bottom third or so of the pot is lava rock or pea gravel for smaller items keeping the peat/sand mix just above the water line where it will still wick it up just fine.
Main idea here is: do not put any un or under decomposed organic matter underwater! If the plant survives, it will be in spite of and not because of the worm poop, bat guano, blood meal or whatever it was you added to the above. Pealite, gravel, Flourite, inert stuff -- OK to play with.
Let the plant get it's nutrition from fertilizer and put that organic stuff in your houseplant's pot above water where there's enough oxygen for it to behave as you intend.
I'll throw some (1-2 tsp) resin coated time release on the surface once or twice a year and I also fertilize with liquid Dyna-gro during the growing season when I do my orchids.
I've got a 10 inch pot just packed with parva growing in only this sand and peat mix and can pull off runners to do submerged aquascaping anytime I want. A week later you'd never know any were missing they grow back so fast.
Interestingly, the plant started to flower only after the pot became full and a little root bound.
Bobo in South Florida