Both Schedule 40 and 80 are reef safe (safe for potable/drinking use if manufactured for this purpose). The difference is the thickness of their walls. Sch 80 is thicker then Sch 40, so if you're using the same outer diameter pipe (say, 1"), the Sch 40 will pass more water then the Sch 80. PVC glue will work the same on both, and since PVC parts are specified for O.D. dimensions, the parts are interchangable.
always us ehte thicker one. it dosnt flex as much and is stonger. ( dosnt crack as easily.)
so what its a few cents more expensive. but its worth it.
especialy if you wanna try and use heat to bend the pvc like i did
I prefer Sch 40 myself. The thicker one really adds a lot of head pressure to your pumps. I've never had a Sch 40 crack on me before. I wouldn't ever try to bend regular PVC of any schedule; there's flexible PVC (Spaflex) for that purpose.
I prefer the 40, only reason I ask is I won a bulk lot of pvc fittings, something like 150 pcs for $25 after shipping and I got a great deal if I can use 80, ripped off if I can't. Since they are interchangeable, mostly will be used for 2" drains, and the 6" parts for a skimmer I'm good to go