Overflow teeth distance

[marietrg]

I'm having trouble with surface scum. It's an oil like substance. I think mainly it is related to a cyanobacteria cycle I'm going through. The problem is the surface scum is not going through the the overflow. The overflow has plastic teeth that are about 2-3mm apart. I'm wondering if the distance between the teeth is so small that it is impeding the oil from flowing through in some way. The other though I have is the surface scum is cyanobacteria and won't go through the overflow. Maybe it is also a surface agitation problem. What do you think?

[thegrun]

Increase the surface agitation. Does the water fall 1/2" or more after it pass through the teeth into your overflow? If it doesn't fall at least that much, surface tension on the water will not allow the flow to pull the scum on the top of the water through the teeth. I prefer 3/16" wide gaps in the teeth, but my 50 gallon tank only has 1/8" gaps, so I need to be sure I maintain a 3/4" waterfall behind the teeth or I experience the same problem as you.

[marietrg]

Thanks for the feedback. The gaps in the overflow's teeth are 1/8". The water falls about 3/4". I adjusted the water returns to create more surface agitation so we will see how that helps.