C-bur, diffusers are always of great debate, Ill give you my 2 cents.Synergistic diffusers and namely AES great lakes models are very well built for a stone type diffuser.The ALA4GL 4 stone requires 1.5 - 2.4 CFM to properly perform. AES tell me that this unit will turn over approx 1250 GPM at 12 ft depth.Stones have specific cleaning instructions and will need to be replaced from time to time and usually have a 1 year warranty. I have this unit on display in one of our ponds."MOST" rubber membrane diffusers are made for the wastewater industry and require a lot of CFM to to supply good water turnover. Most rubber membrane diffusers do not have published turnover rates at different depths at a given CFM.Now for the spam. If you will look at the turnover rates (tested) on a Vertex coactive airstation you will see that it will turnover 2778 GPM at 1 CFM in 12 ft of water compared to the above airstone at 1250 GPM with at least 1.5 CFM.This airstation never needs to be removed to be cleaned as is self cleaning and has a 5 year warranty.Rocking piston pumps are usually used where you have water depths of 35 ft or less and do operate with a higher noise level.A rotary vane can be the pump of choice as it is quiet and easy to work on, and small ponds can be aerated for as little as 1/4 HP.Most vanes operate in 25 ft or less So depending on the goals and size of pond,nutrient levels water source etc etc a system is normally sized to the pond owner vs a one size fits all.Water turnover is one of the most overlooked items when considering a system.If you know that your pond has x million gallon in it and a good turnover rate for your pond is max twice per day the math will dictate what you need to get the job done. You will want a system that will turn over the most water with the least CFM.Do your homework continue to ask the tough questions and always make your decisions informed ones. If you need any specifics feel free to visit vertexwaterfeatures.com or my mail at [email protected] as I try to keep my spam to the minimum on PondBoss.Ted