plants turning yellow
all my plants in my 20 gal tank are turning yellowish i'm using a diy co2 my light is t5 ho bulb color is white and blue my plants are swords,anubias marble queen sword hygropilia kmopakt. aside from co2 i put nutrafin gro every week. please tell me what the problem is. thank you so much. i forgot to tell you that i'm using gravel as my substrate.