Someone I was talking to said that they cannot keep plants, they look good for the first little while and then they turn yellow and die. They wanted to get a CO2 injector but I didn't know if that would help. It is a 20 gallon tank that they have and it is lighted with the standard 25watt tube that comes with a starter kit. They add iron and other plant fertilizers but the plants still die. Would a CO2 injuctor work? (it is not heavily stocked and she does not have fish that eat plants).