I finally improved my success rate with rooting roses and other plants to almost 100% by using a good light set up and finally getting the medium and moisture right. My question though is this. Since I started rooting my cuttings under lights, I have green algae growing on the top of the growing medium. It is the same whether it's the perlite mixture for cuttings or potting mixture for after cuttings have rooted. I have them under 2 T5 bulbs. It doesn't seem like the algae is effecting how anything roots or grows. It's just on the very top of the surface, but eventually becomes a solid green cover of the stuff. This has been with completely sterile mixtures, so I'm not even clear on where it comes from. Since it doesn't seem to be effecting how the plants are rooting or growing it probably doesn't really matter, but it is a little unsightly. Is this common?