Some of marine pics might help Vaughn, most of this comes from there:
Older:
http://www.reefcentral.com/forums/showthread.php?threadid=966407
General google search:
DIY needle wheel impeller - Google Search
So you can use various materials, DIY impellers are cheap and you can always add the old blades back or buy a new impeller, so you can play around for peanuts really.
Another idea is to take impeller blades off a needle wheel and slip those on to the magnet impeller housing of your powerheads etc.
There must be 400 ways to dissolve CO2, but each has a trade off.
When you approach how you want to add CO2 to the tank, you need to sit down and figure out what you want and like.
and what you do not.
Bad:
I hate cleaning disc.
So cleaning little is good.
So is reduced flow over time.
In the tank.
Need flow, and place it in the direction of flow
Good:
Lots of mist I can add inside or dissolve mostly prior
Fast response time between adding and effects in the tank
Out of the tank
Reliable
Active, no need to place in the direction of flow, already has flow
Small
In line
I can all sorts of stuff inside the tank with a powerhead etc.
But I do not want something in the tank.
Nor something large
So stepping back for a minute and thinking about the big picture helps.
Now you can think about a design that will suit
your needs/goals.
Some might not care about a powerhead in their tank, it's for a plant farm, they just want something easy and cheap.
Not everyone is like that though.
My issue is developing a good method like this that works in line with a cansiter filter that folks can DIY.
Mazzeis are great for larger tanks, but they do need pressure, pressure I'd rather not give up if I can help it.
I do not mind some loss.
So you can loop a smaller external pump with a return line and add a needle wheel impeller.
That would fit the bill.
Here's a small pump(you can look around for others):
Hydor SELTZ L25 Pump 265 gph (Saltwater Aquarium Supplies > Water Pumps > Submersible > 0 - 500 GPH )
External operation, fed the CO2 into the loop prior to the needle wheel pump.
The in/out of the flow for the needle wheel should not affect the overall flow of the CANISTER AT ALL.
It just grabs water in the line and adds it back at a certain rate, the pressures should be the same, actually slightly higher at the end closest to the return.
This circumvents any Venturi issues for smaller tanks and cost a little less.
It also has no flow drop or pressure drop associated with it.
Just buy an external small pump, mod the impeller, and you are done.
Add in line in a loop in your canister set up, use those in line quick discconnect they sell for you canister to Tee off and control the flow to optimize the CO2.
Main return line_________________
I I
X----------------
The solid line is the return line, the I's are the Tees.
The X is the pump with the needle Wheel, and the other I is the return to the main line.
It's fairly easy to add a tight fitting seal from air line to canister tubing for CO2 injection port. Cut the hole extra small and heat a bit, then work it into the canister return tubing very tight, this should be water proof to about 15psi.
Some places sell small Tee's with 1/2 ID and air line size Tee ports.
Adding some E6000 glue over this can help and that stuff is good for sealing up pesky leaks. If you glob the E6000 on there, then wrap the glue in plastic wrap to get a good seal, this can help.
Add a check valve to the CO2 line obviously.
Rex Grigg sells very nice brass check valves among other things that might be of use to folks.
This is what I plan on adding to one of my tanks that lacks a sump.
The cost of the Octopus is that of most powerheads and it has a nice needle wheel already, so for the $ and the application, I have a hard time beating it.
Sump flow rates are also much more consistent than canister filters and a good surface skim is always nice.
So for some tanks, it works well in line, some, I can add to the return port.
Easier for the sizes I deal with than mazzei.
Mazzeis are more useful I think, given the trade offs, for larger tanks or folks who like to mess around.
I can still get similar if not better results with needle wheels and use less electric and flow loss.
If you are not using say 20-40% of the pump flow, then mazzeis are good for larger tanks.
I think it is important to note, that one is not better than the other really, they just have trade offs.
Listing the advantages and disadvantages fairly to anything is the key to good advice.
Regards,
Tom Barr