Low light, slow growth tanks usual requires little to no extra fertilization.  The rate of nutrient uptake by plants are quite low, and fish waste usually provide sufficient nutrients for this kind of setup.  However, if you noticed that your plants are no longer healthy green, or the old leaves are turning abnormally yellow, we recommend slowly adding our GREEN fertilizer.  GREEN is a concentrated mix of macronutrients which supplies plants with needed Nitrogen, Potassium, and Phosphorous.