This is the pump curve for the Blue Diamond ET120 ( I assumed the ET model)...

[Linked Image from forums.pondboss.com]

I have added the pressure equivalents in psi in Red at the bottom and made red circles on the flow axis that correspond on the left. The maximum depth that this pump would run a single diffuser is about 8 foot deep. This calculation in based on the required 0.433 psi per foot of depth of the diffuser and assumes about 1 psi of line losses combined with the pressure required to operate the diffuser. Find the "1 CFM" mark on the left and follow the line across to the right until it hits the curve for the ET120, then drop straight down and you will find the pressure at which the pump will be operating...4.35 psi

The calculation: 4.35 psi (taken from the curve at 1 CFM of air flow) minus 1 psi for line losses... all divided by 0.433 psi per foot water depth = 7.7 feet.

This concludes that this pump will run a single diffuser at 8 foot deep and supply 1 cfm of air to it. If you add an additional diffuser at 8 foot deep, the CFM (airflow) will be reduced by half. Most commercial diffusers like 1 to 2 CFM to operate well. You would not be gaining much water movement, if any, but you would be spreading the water movement out across the pond given that you positioned them far apart. I would not recommend this approach. We need to run the numbers to see if a single diffuser can effectively turn the pond over. Give us some basic dimensions, & basic shape of the pond, then we can estimate the number of gallons in the pond. This will help determine if a single diffuser can turn your pond over effectively. Rule of thumb is at least once a day.

Attached Images
ET120 Curve.JPG
Last edited by Quarter Acre; 03/16/21 08:56 AM.

Fish on!,
Noel