why does it overflow?

I have 2 mis-matched HOB overflows on my 125 - its ghetto and will be upgraded one of these days :. The older one rocks, it skims the surface like a champ, is always cascading, and I never have any problems air bubbles in the U-tube - they get in the tube, but are promptly sucked out and down to the sump. The newer one looks a lot nicer, but does not draw the same amount of water despite having the same size drain, and bubbles keep congregating in the U-tube slowing it down even more.

Today I was playing around with them, switched and cleaned the U-tubes, played with the sponge filters, and then I read somewhere it could be a lack of flow. No problem (i thought) as I had a spare quiet one 4000 lying around, so I hooked it up as a 3rd return and as soon as it went on the old overflow lost its cascading effect almost immediately and started overflowing onto my floor behind the tank.

Any ideas as to why this happened, or how to fix the origional problem of bubbles in the newer o-flows U-tube?

Thanks.

~Will.

 

Have you tried lowering the overflow that gets the bubbles in the u-tube. Mine would do that when I first put it on and was adjusting it and I lowered it because the water falling into the overflow had to drop a good bit and was creating alot of bubbles and going into the u-tube.Lowering the overflow raises the water level in the overflow and water doesn't have as far to fall and you have alot less bubbles.Also what gph is your pump and your overflows?

 

Both overflows are 600 gph each (1" drain) and my return is just above 1000 gph after all the bends and head loss. Thats why I figured more flow might help. Its an acrylic tank so both HOB overflows are stacked up to the top of the tank and the water level is about 1" - 1.5" below the build in lid. The old overflow has a nylon screw to fine tune height adjustment. The newer one has small clips that it snaps into as pre-set intervals, if it goes too low I risk a flood in the event of a power outage.

~Will.

 

Sounds like the different overflows being mismatched is the problem. I would get two the same where you can dial them in together(get the right height).Not being able to lower the one is creating to many bubbles and sucking them into the u-tube and losing syphon.Can you cut your flow back on the pump and just use one overflow till you get the same overflows?

 

matching them is the plan for later, but right now i'm completely confused as to why the single overflow (the one that works great) started pouring water on my floor right after i hooked up the 2nd return pump.

~Will.

 

Sorry about the little lake that you formed. If both overflows are the same( in every way) then have you checked to see if theres a shell blocking the return tube? That happened to me once and it turned out that there where 2 shells blocking the drain.



Luna

 

2nd pump may have put you over the gph the overflows could handle.

 

thats not a bad idea luna, i'll plunge it when i get home with my custom U-tube cleaner - a toilet brush with 1 side cut making the ultimate pipe cleaner.

if the 2nd pump drove too much water up, wouldnt the tank have just filled up to the top, then over flowed?

~Will.

 

woot, got both overflows tuned to match each other and all air bubbles that make their way into the U-tube get pushed right through. still totally confused as to why that 1 overflow box spilled water onto the floor like it did after that extra flow was added. but now I could care less as I wont have to check that dam U-Tube daily anymore.

~Will.

 

Acrylic tank with HOB overflows? You should just drill two one inch bulkheads into the back of your tank and put intake guards over them.