Hygrophila corymbosa compact

Hello,
I have aquired a large amount of Hygrophila corymbosa compact. I have well over 100 specimens, maybe 200 if I split them again which I plan to do. I dose via EI & am experiencing a infestation of brown diatoms - brown gunk! There is also some black stringy stuff which I think is BBA. This is in a standard 55 gallon tank with a Koralia for circulation.

Does anyone know if Hygrophila corymbosa compact is a heavey feeder of any particulary macro or mico nutrient needed.
these are the water parameters
temp- 80
PH -0 6.5
Ammonia - 0
Nitrite - 0
Nitrate - 40 +
PO4 - 0.5
KH - 7
GH - 12

Nitrate is quite high, I am thinking to lower it around 20 ppm.

My lighting is DIY 4 X 55W with two 6500K , a 8000K and a 5000K CF bulb
Substrate is oil dri. Pressurized C02 - 3bps.
I do use Osomocote in gel caps every few months ( set deep into substrate). Filtration via an Eheim 2217. Heater is an ebojager.

Any tips from a Plant geek?
I hope so- Thx :~)

PS *** I have seen others reply with.. "nutrients, lighting & CO2 are out of wack". Although it may be true it is not too helpful if your stuck like I have been with this problem for months