Hi everyone:

I've got a 90g display with a 30g sump. The main return pump to the aquarium is fitted with a shut-off valve in-line that allows flow control back to the main tank.

My problem is that when the valve is all the way open (which I'd like to do), it generates too many air-bubbles in the return water. Because of this problem, I have to dial down the valve to about 3/4 on.

If you look at the sump (which is baffled), the only real bubbles that are generated are by the return flow and, of course, my protein skimmer (which does generate lots of bubbles).

Any ideas on how to accomplish full water return without bubbles?

Thanks,
Adam

I heard something about submerging bioballs do disipate bubbles. I'm gonna try it near my tank overflow.

water quickly passing over bio-balls is actually more likely to create air bubble than dissipate them.. it may make large bubbles smaller, but i dont think will dissipate them.
in fact this is actually how some downdraft skimmers create micro bubbles

Making a few assumptions, however these tips may help.

I assume your skimmer is creating the bubbles, if so how is your skimmer returning its water back to the sump?

One tip that works is run the skimmer water output over for example a stepped Perspex sheet, I used this in the past to remove micro bubbles from a display tank, that had a HOB skimmer, that was introducing bubbles.

Imagine a flat per Perspex sheet, with ridges stepped all the way running from left to right like the steps on a ladder, I made the ridges using beads of silicone sealant. Running the return water flow over this will beak the micro bubbles.

Next tip, that has helped me in the past, is if you only run one return pump try running two at half the flow rate of the single you are running so if you have a 6000 litre per hour single return, replace that with two 3000 litre returns, it gives the bubbles slightly longer to dissipate in the sump before being returned to the tank but you are still moving the same volume of water.

Probably help more with a better description of your setup.

Cheers

Nath.

I wonder if the connector you are using on the low side of the valve is allowing air to leak in when not under heavier pressure... by closing the valve you create backpressure which would tend to not let the air leak in as easily, resulting in less bubbles... or I could just be smoking crack...

One easy way to find the culprit could be to shut off the skimmer and crank the valve all the way open...

Thanks to everyone. I actually manually tightened every connector on the return line to the tank by screwing the lockwasher down tighter. Much less bubbles.