Look at the dosing table Seachem supplies for their products, then dose at least twice what they recommend. That will not cause algae. I don't know what your tank dimensions are, but 4 x T5HO is really a lot of light, probably much more than you should have. Unless you have a $2000 CO2 measuring probe, you can't say you have 24 ppm of CO2 in the water. If that comes from using the KH/pH, ppmCO2 table, it is a meaningless number. You need a drop checker, with 4 dKH distilled water in it, to help you adjust the CO2 right. Right now, you probably have closer to 10 ppm than 30 ppm, and that won't work with high light.