Purple/green sandbed

[actorrs]

Why my sandbed looks like this?

 

[Nano sapiens]

This is quite typical/normal. Different types of bacteria and micro alga will colonize your sand bed and those receiving light up against the glass panes can photosynthesize. You should see small bubbles of respired oxygen due to respiration during the lighted periods.

 

[Cole.mormon]

Cyano but I doubt it

 

[Cole.mormon]

Probably micro organisms or corraline