Tips on prime'ing HOB overflow?

[TangoTank]

My overflow tube from overflow box to the box hanging on the back of my tank is sometimes bubble free, then gets a giant bubble near the water level in the tube in the back box!! I hope this makes sense. Are there any tricks for getting that out?? It causes my flow to be too slow which causes my return pump to run half submerged in the sump-refugium thus spitting air into the DT causing salt creep. Urrrggggh :\

 

[melosu58]

I used to take the J tube and just bang it in place and the air bubble would disapear.

 

[TangoTank]

I used to take the J tube and just bang it in place and the air bubble would disapear.

Hmm... I've tried that. Thks thought for your reply.

IDK what the prob is \ I was hoping there was something out there I just didn't know yet.

 

[Ingy]

many HOB overflow boxes come with an aqualifter pump to eliminate the bubble. Fortunately I don't have a HOB overflow so I don't need to worry about it. not do I know much more. Check out the CPR overflow delux for more info.
I think somebody here has built their own aqualifter, but I know nothing more about it.

 

[Daniel Fishy]

I have a eshopp hob if you match the flow and return the air never builds up. Can you increase the return flow? That will speed up the overflow. What size is your return pump and overflow bulkhead?

 

[mr_X]

The reason you are getting a bubble in your J tube is that your return pump is not matched with it. It needs more flow going to it.

 

[navaljonf]

Easiest thing to do is get a j tube with a smaller diameter. The water will have to travel faster and will prevent large air bubbles from accumulating (same concept as adding a larger pump to your return)

 

[mr_X]

Then you are defeating the purpose of having a overflow rated for X gph. Bottom line is you aren't accounting for head loss.
that said, you can shove a piece of airline tubing up the short end and suck out the trapped air....but you'll be doing this again......

 

[TangoTank]

Thanks for all the replies!

Then you are defeating the purpose of having a overflow rated for X gph. Bottom line is you aren't accounting for head loss.
that said, you can shove a piece of airline tubing up the short end and suck out the trapped air....but you'll be doing this again......

Ok, so my return pump is too powerful for my down flow from the overflow?

Edit: So should I get a larger J-tube??

When I was noticing the pump was running low on water in the sump-refugium, I thought that & the LFS said no, that pump is right. So I thought the flow down was too slow so I was cleaning the back overflow box sponge daily. Then I thought maybe it was the filter sock in the basket slowing it down, nope! I thought it was the water level in the DT (which that does affect it but I've seen the tank a cm or more lower than I thought it could stand & the sump level was pretty high!) Seems there's no rhyme or reason, I only recently noticed that every now & then quite a bubble forms in the J tube near the water level in the back overflow box which I'd call more of a U-tube!

I didn't know if maybe there was some trick I didn't know yet.

 

[SaltwaterNuB]

Ever thought about and aqua lifter? It'll work too. What X said will do the trick as well.

 

[mr_X]

If you are getting an air bubble, the flow is too little. Turn UP the pump, not down. What is your overflow rated for and what is your current pump?
It has nothing at all to do with the height of the water in the DT. That should never change if the sump is running. All fluctuations will happen in the return area of the sump.
There is rhyme and reason.

 

[TangoTank]

If you are getting an air bubble, the flow is too little. Turn UP the pump, not down. What is your overflow rated for and what is your current pump?
It has nothing at all to do with the height of the water in the DT. That should never change if the sump is running. All fluctuations will happen in the return area of the sump.
There is rhyme and reason.

Ok, thks! I will need to find that out about the return as I bought this set up used. The pump is 640GPH for a 75g tank. How can I find out my overflow rate? Maybe I should try cleaning out the tube to the sump?? I hadn't thought to look there til now. It's an opaque tube, so I kinda just don't think about it.

 

[mr_X]

If light can't penetrate the drain, it's not likely that it will be clogged, unless there is a snail shell stuck in it or something.
640 gph after head loss is probably around 500 gph or so. If your HOB is a 600 gph overflow, there's your problem.

 

[TangoTank]

If light can't penetrate the drain, it's not likely that it will be clogged, unless there is a snail shell stuck in it or something.
640 gph after head loss is probably around 500 gph or so. If your HOB is a 600 gph overflow, there's your problem.

Ok, thks! I'm going to do a test on my overflow to see how fast it's flowing. My LFS told me how to do it. So... if my overflow doesn't match my return, that's the prob?? So better to speed up overflow to match return rather than slow the return?? I haven't had a bubble show up lately. That's why I say there's no rhyme or reason! I'm sure there is a rhyme or reason, I just can't figure out what it is. My LFS said make sure the J-tube isn't near the back box's down spout b/c if it causes like a whirlpool effect, it could be throwing some air up the j-tube.

 

[mr_X]

I think your pump is too weak for your overflow. I'm betting it's a 600 gph overflow and your pump after head loss is less than that.