Your diffuser looks like the Eheim diffuser. Some of us have had a lot of trouble with the check valve that comes with it. It seems to actuate at about 15 psi. What I did was replace the check valve with a Tetra check valve. It has almost no back pressure. You can test the valve by trying to blow into it. If you can't you may be better off replacing it, especially if you are using DIY low pressure CO2.
"I use an eheim diffuser from drsfostersmith.com. Seems to work very well."
Sir_BlackhOle, is the incoming CO2 line just hooked up to the diffusor and that's it. Seems way to simple.
I've been looking for a good diffusor and have tried several but I don't like a lot of ugly equipment inside my tanks and most of those that I've used are the large cylinder type such as the Aqualine Buske diffusor. This Ehiem looks like the answer that I've been looking for.
You will probably have to bleach the glass difusser disk once a month to clean it. It is held in place under the dark plastic top which screws off. The disk is held in place by a rubber washer.
The disk is rather fragile! I have never broken one but be careful and it should last forever. Carefully pry the rubber washer out with the disk still in place. After the disk and the rest of the parts are bleached rinse them off and carefully put the disk in the rubber washer and this assembly into the housing. Works like a charm. Be sure to fill the lower clear housing with water before putting the disk in place, so the bubble counter will work.
People claim these difussers are not efficient because often the bubbles reach the surface. However many small bubbles have a much larger surface area than one larger bubble with the same volume (as is often the case in a reactor). Also as the bubbles rise the pressure is less and the size of the bubbles increases, so the fact that the bubbles are not as small as you think they should be is misleading. Also I am told that as CO2 is absorbed in the water the bubbles are absorbing oxygen and nitrogen, another reason why the bubbles don't disappear. So I find this diffusser almost as efficient as my 3 inch diameter 3 foot long reactor. You can guess which I like better.
I use it with my DIY co2. It will NOT work with the check valve that comes with it. I find that the bubbles are too tiny to break the surface tension of the water, so they stay at the surface untill they dissolve.
20g - CO2 is fed into custom intake for Fluval 104. No longer working as I've had to increase CO2 and this now results in air pockets developing in the filter which then surge out into tank every few minutes. Almost done with a DIY PVC reactor which I'll be installing soon.
2.5g - fed into a modified Azoo mini palm filter. Drilled hole in side of pump & glued in a rigid air tube positioned to place bubble right into impeller area. - works, but is too noisy.
15g - 'Mini vortex' power reactor - works good, can't hear it, but is an eye-sore in the tank.