30 gallon (US) tank; tetras and pictus catfish, 2 gouramis and 1 large Plec. Ambient temp 78F; Nitrate= 10 ppm; Nitrite = 1 ppm; hardness (GH) = 180ppm (you try getting soft water in THIS area of W Texas, lol);Alkaline 100 ppm, PH 7.6.

PROBLEM I have 2 CO2 bubble diffusers at each end of the tank, ONLY plant that actually LIVES is hogwort (floats on water surface, won't grow, but just "exists", EVERYTHING else just withers and dies ! Gravel bed is small regular gravel, no other substrate approx 2-3" deep.
I add "Flourish" Aquarium plant food with every water change, but still no luck. What am I doing wrong here ?