Salty

As many of you already know, I am trying to establish a plant tank. I had 2 CO2 injectors in my 30 gallon, but there was such a build up of algae, that I took one out. A friend suggested that I use a plant fertilizer also & told me Plant Gro was a good one. As per directions, I put in one capful/10 gallons of water. However, there were no directions on the bottle as to how often to put it in. Can anyone help? Thanks.