Having some trouble getting adequate airflow to the diffusers (air stones) in my deep water culture beds. I have three DWC's 1.2M X 18M, with 17 diffusers each for a total of 51 spaced roughly every meter down the length of the DWC's. The water depth in the DWC's is a constant 20cm (8"). I am running two 60 M3/hr ring blowers. Appropriately sized PVC pipe connects the centrally located pumps with a length of PVC that runs down the side of each DWC. Each diffuser is connected to the PVC pipe via a one meter length of 1/8" airline tubbing. The diffusers are 10" long by 1/2" wide, encased in plastic, but open on one side.

I was barely getting any airflow from the diffusers with one ring blower, so I recently added a second. There is some improvement with the second blower but the performance is still disappointing.

I have confirmed the air filters are clean and the airflow from the blowers feels appropriate in terms of strength or volume.

I understand the ring blowers are not suited to develop very much pressure but I would have thought 20cm of water would be acceptable.

I am wondering if it's an issue with the diffusers? They are about six months old but don't seem to be any less effective than they were originally.

I am reluctant to add another blower as my electricity allotment is already reaching it's maximum. Especially without evidence that this is the problem.

I understand a diffuser consumes roughly 0.3 cfm. So, if I am calculating correctly, 0.3 cfm X 51 diffusers = 15.3 cfm required, and my two blowers produce 60 M3/hr, (1 cubic foot = 0.0283168 cubic meter). This works out to 0.43 cubic meters per minute, or 26 cubic meters per hour required for 51 diffusers. Considering each blower is providing 60 M3/hr in theory, I should have over four times the airflow required. So what gives? Is 20cm of water too deep for a ring blower, are my diffusers cheap Chinese junk, or is it something else?