Can someone please explain this...

[wlam18]

I have a 20G sump with some macro algae with 13W NO. I only leave the light on when the display tank is dark. Lately I found out if I leave the sump light on 24x7, I have less algae on the display tank glass. Why?

 

[RMPD109]

The 24 hr lighting is keeping your macro algae consuming the excess nutrients all the time. With the light off the macro only feeds on the nutrients for 12 hrs it is lit and not the 24 as you do now. That leaves 12 hrs for nuisance algaes to consume nutrients.

 

[wlam18]

Any down side to leave the sump light 24x7? other than the electricity bill...

 

[RMPD109]

Some types of macro require 24 hr lighting. Just remember the bulb life may not reach maximum length. You may need to replace more bulbs more often.

 

[malkore]

good answers RMPD. you got yourself some Kudos!