Water imbalanced all of a sudden, help!

[New2Reefing]

I'm really confused......my single overflow (u-tube) was returning the water fine on my 55, and being returned by a mag 5.....recently, the top has been full to the brim and the sump empty...so i started another siphon......the second utube helped for all of five minutes, then the top filled again, sump still empty......both overflows active........what the heck gives?

 

[kau_cinta_ku]

sounds to me like something is clogging the drain and your pump is pushing more water than the overflow can handle. what size are the overflows rated for?

 

[Tommyc]

do you have a gate valve between the mag5 and the return? any large bubbles at the top of the u tubes? sponge filters between the utubes and the overflow to the sump? need more data.