Thanks for all the replies!
Originally Posted by 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......
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.