Tank almost overflowed.

Most time the cause of this is from an undersized return pump, or the u tube becoming dirty with algae and allowing air bubbles to become trapped and then braking siphon.
Yep that return pump is to small and its allowing bubbles to accumulate.

 

Do this he has the same box that you have it work good for him and he had the same thing that you had hope it helps


YouTube - How to - Aquarium overflow / sump / refugium. Some tips

 

yes slow flow can be a problem but also with that type of overflow bubbles can build up over time most ppl slove that problem by purchasing a aqualifter vacuum pump .whats wrong with smaller return pump is that with a correct size return pump most of the bubbles are simply swept threw the u tube with the water .too small a pump and air stays in the tube .does these happen alot or every so often ?

 

i would get the correct size return pump and the aualifter for a backup also make sure u measure how many feet up the pump will have to carry the water and get a pump that can pump x amount of gallons at that many feet

 

One thing that would be cheaper is to just get a smaller U tube, if yours is 1-1/2" then you could try a 1". This would cause the water that overflows to move faster through the tube and hopefully carry those bubbles away with it.

 

My U tube is an 1", The hose that runs it down into my sump is around 1 1/2"

 

Yes a smaller u tube might fix your problem, with the u tube you have you would need a pump of 600 to 800 gph to match the size of tube you have and then install a ball or gate valve to fine tune it to match the over flow.

 

Could try a 3/4 tube then I have seen them at my LFS but not sure how easy they could be for you to find.

 

Great Video!! I deff wanna try that. Thanks!!;D

 

keep us posted if it works