oh, mine also had a shaft but has room for the screen.
i don't know if it worked for supercoley.

i tried tying up a screen to mine, and run the motor into a basin, cant see clearly the whether the bubbles produced has any difference in size though. the reflection of the water makes it hard to discern.

The 'screen' thingy was from someone elses tank as was the marine bubbles picture. I never tried this method. I have in fact gone away from the whole needle wheel concept as is descrived in this post and rather than geting the MP400 to suck in the bubbles and chop them up I have positioned it to blow across the top of my ceramic diffusor which then distributes the bubbles all over the tank.

Is working exceptionally well for me at the moment.

I never really had a problem with the Rhinox 2k diffusor, but was experimenting with this method which did work well. The new position just sems to work better and as the bubbles are nice and small from the Rhinox they don't really need chopping up any (I bleach clean the diffusor disc weekly at water change time)

Andy

@supercoley
so you're saying the the needle wheel concept described in this thread worked well with you too?

I've gone pretty much all venturi as I can take the powerhead out of the tank entirely whether I have a canister or a a wet/dry sump etc.

Since the venturi is in line or feed into the return pump, the mix and blowing around of the mist is already in one efficient flow source.

No need to add something else in the tank.

Also, for smaller tanks, a simple Adaptor tee works well and does not reduce flow rates at all. If you have a longer return line, then the bubbles will get more dissolved and ground up, larger tanks with more pump power: mazzei work well.

Sumps can be feed from a dual needle wheel impeller style method, feed the CO2 into a small powerhead or needle wheel Gen X pump, then feed the outflow directly into the main return pump intake.

Or you can use a small mazzei(still need the pump to drive it, so may as well use a needle wheel for this)

If you like a diffuser disc in the tank, then that's fine as well.
But they all do the same thing when correctly set up.
For smaller tanks without canisters, the disc are fine/practical.

Regards,
Tom barr

thanks for that info tom
when you say that the venturi is in line or feed into the return pump, do you mean it is tightly piped to the intake of the return pump wherein the return pump only sucks water from said venturi.... or would the return pump suck air from said venturi as well as from other portions of water in the final compartment of the sump?

also, i would appreciate if you can explain what is a mazzei....?
sorry... im a newbie hehe

im planning to just put the co2 injected directly at the intake of my rio 2100 pump... and the return pipe is around 6feet distance from the pump output....
do you think this is enough to dissolve the co2 into the water and allow plants to maximize absorption of it?
by injecting directly into the return pump, it makes me have less equipments to maintain and makes the whole system simpler.... and also i wont need to rig up something like the venturi whether in the sump or in the tank, since the materials are not readily available in my part of the world....=)

your comments will be highly appreciated...

regarding the mentioned adaptor tee, do you mean a tee that is in the return pipe?
could you elaborate further?
sorry i kind of didn't understand this....

or do you mean a tee placed after the venturi reactor?