If your DIY hood is painted white inside, you probably have around 60 micromols of PAR, which is medium light. With that much light the plants would grow pretty fast if they had the nutrients they need, nitrogen, potassium, phosphorous, trace elements and carbon. Your DIY CO2 should be adequate for carbon, but you need to dose the others. See _Dosing Regimes_
for a very good way to provide those nutrients. When the plants can grow as fast as the light drives them to, algae usually don't start growing.