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Looking for an answer for two questions about sponge filters.
1. Does the length of tubing that comes out of the top of the sponge make any difference on efficiency, as long as it's not out of the water of course.
2. Is it better to diffuse the air into tiny bubbles, or just keep the end of the air tube bare and have large bubbles.
Thanks for any help.

Tiny bubbles or large bubbles are not really the issue...

What the issue really is, are the bubbles moving the surface of the water where all gas exchange takes place??

What really creates oxygen in the water is the constant movement of the surface water allowing carbon dioxide out and admitting oxygen in.

You can adjust the bubble flow to create the best surface movement available.

Remember, contrary to popular belief, bubbles alone flowing up through the water do not add oxygen to the tank.

--garyroland.

--Vero Beach, Florida.

Thanks Gary, but I acualy knew that already.
The bubble size question relates to the efficiency of the sponge filter, not so much the gas exchange process. In other words, will hundres of tiny bubbles create more "pull" through the filter than three large bubbles, or vise-versa, maybe no difference at all?
The tube size question is the same, will a longer/shorter tube create more suction?
Thanks again all.

Tubes need to be long enough to create the flow of water, a really short tube would be very inefficient but beyond say 10x the tube diameter you probably don't get much gain in water flow for volume of bubbles. But a longer tube won't hurt anything either as the bubbles don't really lose any power or velocity on their trip up the tube. I'd just make the tube as long as practical.

I suspect smaller bubbles move more water up the tube by virtue of their greater surface area. If you had 1 1cubic cm bubble and 1000 1cubic mm bubbles the 1000 mm bubbles would have more surface even though they both have the same volume.

For the sake of easy math we'll use bubbles in the shape of a cube. A 1 cubic cm bubble has 600 sq mm of surface. A 1 cubic mm bubble has 6 sq mm of surface but you multiply that by 1000 and you've got 6000 sq mm of surface.

Mike

I find the filters with the air stones (tiny bubbles) on them are always more densely filled when I clean them then the ones designed with out the air stone hook-up (large bubbles). The longer the lift tube as well seems to generate "more pull" because it acts like a vortex.