I see a lot of wood chips and bark in your soil. It's a common misconception that these types of organic soils are nutrient rich. This is only the case after the organics have broken down and have been mineralized. You get an initial nutrient burst from the composted cow manure or pasturized chicken litter but after that initial period the potting mix is spent. The organic soils we use are useful under water because plants supply oxygen via the roots to the bacteria that break down the peat, bark, humus, and other organics in the potting mix.
Anyways, my suggestion to you is to use some liquid plant food and spray the anubias.