Overflow U-tube bubble - why now?

[trippclark]

Okay, I am hoping that one of y'all bright people can help me figure this out.
My overflow has had the same exact U-tube for 8 - 10 years, and the same Rio 2600 return pump for the same amount of time. During this time, I have probably only had a bubble develop in the U-tube maybe 4 times. In the past, the only time I ever had to mess with it was when I would clean it.
Tonight, I have a big bubble in it, that is restricting flow -- and this is the third time in 10 days that I have had to get the air bubble out. And the only way that I know to do it (I'd love to find a better way), is to run small airline tubing through it and suck the air out and create a vaccuum (and get a mouth full of saltwater half the time).
Anyway, after reading some other posts, it seems like I may can correct the problem with a smaller diameter u-tube; but I can't figure out why I am having the problems all of a sudden when before for so many years this overflow & return seemed so perfectly balanced.
Any ideas????

 

[nm reef]

Have you recently changed your return pump? Or is it possible that your return pump has lost some flow rate? I know that in order for a "U" tube to work correctly there needs to be enough flow to prevent accumulation of bubbles...if the flow rate in your over flow has dropped that may be the cause of your trouble.:thinking:

 

[trippclark]

No, that is the wierd thing. It is the same pump --- even the same tubing. No change. I guess it is possible that the pump is wearing out and flow may have dropped off.
I re-made my sump about 3 months ago -- doubling its size and adding on a small fuge, but that was 3 months ago -- this problem just started last week.

 

[cprdnick]

When your water overflows into the ******** box, does it have a turbulent fall or is it smooth? Turbulence in water can cause oxygen to be trapped in areas that do not allow easy escape, such as a U-Tube. If the water is sloshing when it overflows into the box it could be causing your tube to be siphoning some air as well.

 

[trippclark]

I think smooth, but I'll watch it more closely to see.

 

[squidd]

You may want to look into giving the pump a thorough cleaning as calcium can deposit on the impeller and shaft slowing the pump/flow...
You also may want to look into cleaning/changing your pipes/tubes/hoses as they can become restricted with calcium deposits and algae growths inside the tube, restricting/slowing flow...
Even a small amount of "roughage" inside the tubing will cause turbulence which restricts flow...
Lower/slower flow will cause bubbles to be traped in the "U" tube when they weren't a problem before...
Have you started doing any buffer/calcium/Kalk additions lately which may be causing a build up now...??

 

[trippclark]

Yes, calcium additions much more regularly as of late as I have gone from fish only to now inverts and corals.
BTW, I lowered the level on the inside the tank overflow box about a quarter inch and that pushed through the bubble. We'll see if this may have some lasting effect.