How many overflows

If i am only looking for 10x the volume for the sump, and plan to have maybe a 40 gal total volume sump, but use maybe 30 gal of it, then id need 300 gph? Right? or is this not enough flow?

 

40g sump is good, but you want 1000gph+ going through it., if your using a 1200 gph overflow box.

I use a 10g sump on my 55g with 350gph overflow and a 350gph mag3.

 

If you want to save money, drill the tank yourself, and simply buy a couple bulkheads with some PVC fittings.

You can make your overflows exactly how you want them, they will be foolproof (and floodproof unlike any HOB overflow) they will take up less room, and like I said, cost less.

 

He cant drill his tank due to the bottom being tempered glass.

 

Yep That's what i want to do....... But the sticker says Tempered Glass and i understand you cant drill tempered glass.