Stupid Sump question

[Fernzpat]

New tank/system.  I shut down my pumps for feeding and have had no trouble the first few times I did so.  Today the HOB Refugium overflowed into the stand/floor during feeding time (luckily I was right there watching).

 

I knew my return pipe from the HOB was low (I re-did it after first water test b/c it was so loud) but why would it drain just fine the first 20 times and not now?

 

[DSA65PRO]

I need a little more info on your system, internal Overflow? With a Spill dam or Strainers? Pictures will help. Is that a check valve is it in the return or supply? If it's on the pump Supply side you need a hole in your line between the pump discharge and the check valve and it must be above the highest water line you'll ever have in your Sump. This is to let Air out of the line and pump, so the pump doesn't become air bound. It must be kept simple and free flowing at all times. I'm against all valves in the lines to the Sump. A properly designed system doesn't need them, and they are a terrible restriction. Check valves foul quickly and are soon useless. On the water going back into the aquarium you should drill a hole on the elbow, that goes to the line lock flex, at the 4:00 or 8:00 o'clock horizontal position to act as a syphon break. 

[Fernzpat]

Thanks for your detailed reply!  I ended up putting in a small air hole in on the refugium return and have not had it happen since.  Again thanks for the tips.