My 75 gal tank has been set up for about a year now. With 80 lbs. of Eco-Complete under 50 lbs. of pool filter sand. Plants are growing ok but slower which I assume is good. When should I look to be adding fertilizers to it. Have Osmacote in #0 capsules ready to go. How much and when should I start, plants ran out of nutrients last time. Rocks in back have been removed they were limestone.