External overflow problems

[Doglips56]

Ok so we sold all of our large tanks and we’re going to get out of the hobby due to my continued serious health issues but really still wanted something. We decided to convert on of our non-copper QT tanks (a 49g breeder) into a reef tank. Everything is going pretty good EXCEPT this is our first time using an external overflow box and we keep having issues with it suddenly not working properly. Either the water won’t drain fast enough and the tank water level gets super high and the sump gets so low air bubble are getting shot into the tank or the pump isn’t working properly and the water level in the tank suddenly drops and the sump fills to the point of almost overflowing. I desperately need a siphon break. We added a John Guest fitting on the secondary drain on our drilled tank, but not sure if that will work on the clear U tube or not, especially since it’s not like a drilled tank with an emergency drain pipe. We need to do something ASAP before the real disaster happens that we aren’t home to address. Luckily each time there’s been a problem we’ve been able to avert disaster, but just barely.
Any words of wisdom would be appreciated

 

[lapin]

Can you tell us what type/brand of external box you have? and maybe a picture of the drain