I swam out with mask, fins and snorkel, held my breath, dove down the 9' while following the buoy rope down to the diffuser (in pitch black darkness because of all the algae in the water only about 18-24" visibility), and with gloves on scrubbed the diffusers with my hands while they were in operation with air coming out.
Did this when the blue-green algae subsided after a couple of rains and the water looked fit to swim in. Grandson came along for the snorkel.
Never pulled them up. Still need to though, as now two of the three double Matala diffusers only have air coming out one of the two diffusers. The last time I cleaned them a couple months ago only one of the three had a collapsed diffuser.
For some unknown reason, all the air is going to one diffuser and none to the other. The collapsed diffuser is setting flat with the membrane center resting on the internal built in check valve. There is nothing but a simple Tee connecting the two diffusers so nothing to change the air pressure being equal to each diffuser. No internal restrictor like on some other brands, nothing. The only thing I can fathom is that when I have shut the pumps off and back on to flex the membranes to partially clean them, the diffusers collapsed onto the check valve and rubber membrane "stuck" somehow in the middle. Maybe because of the design the rubber in the middle that covers a hole to act like a check valve imbeds in the hole and sticks????? Don't know. Will not know till I pull one of them up. Right now getting ready to go cross country on motorcycle again so likely will not know till later this fall. May just pull all three up for the winter, plug the lines, and leave them out till re-installing next spring.
I'm not too worried about it. The single diffuser seems to move "almost" as much water. It just bulges up a little higher in the middle than the double that is still working. They all get the same cfm of air via three identical pumps, so same air flow just coming out one single diffuser instead of two seperated diffusers (couple inches in the middle).
Yes cleaning them definitely helps. I saw this both last time and this time. My north diffusers always have more crud on them than the south. The middle - don't remember anything special about it. Last time when the water was more clear and I could actually see the diffuser working on the bottom, the clogging had the north diffuser about 2/3 clogged up. The air was all coming out the remaining open holes. When cleaned the bubbles were finer and on the surface I could visable see more water movement after cleaning. This time it was pitch black down there and had to do the job by feel. More modest improvement this time, but keep in mind I cleaned them a couple months ago.
Also cleaned for the first time the singles in my forage pond and sediment pond )they are run by a single pump with a valve to balance desired output). The forage pond was nearly completely scummed over with stuff at least a quarter inch thick. Amazed some air was still coming out of it. The sediment pond was not bad. Have no clue why the difference. I do turn the air down to the forage pond so there is less coming out it because it is only about half the size pond as the sediment pond (roughly 1/20th and 1/10th acre).
That is what I can tell you. I think I will just pull them all when water temps get down past fall turnover and plug the lines. Leave my rope and buoy along with some sort of weight on the air line. Find out the problem with the collapse of one side, recondition, and re-install next spring.
That is "the plan". Sometimes my plans change.
Hope that answers your questions. I made the post long enough to answer 20. Good luck with yours. I think you likely will find improvement with cleaning.