Black Root on Phal
 

Several of my Phalaenopsis orchids have a few black roots. The leaves are healthy and there are plenty of healthy roots. The orchid has a healthy spike. Light (artificial), watering, and fertilizer routine are consistent. Do you know what causes the black roots?

They're older. Might have algae or cyanobacteria growing on them, which is not a problem.

Even if they are just old and died, they will slowly decompose, but that is no threat to the nice, new roots.

Thanks for reply. I will leave them be