Overflow pvc diameter??

[nanomania]

Hey guys, im looking for a 7000lph to max maybe 9000lph flow, can i go for 3 x 1.5" holes or 3 × 2" holes for pvc? I want 2 as main and 1 as sos...

Also i wana add a diy acrylic guard/surface skimmer, how long and big should that be??

 

[nanomania]

Anyone? Plz help