Hi Cecil, In Lindas case with the run of inground hose 500 plus ft I would like to have 1 CFM in the water thus advising a pump in the 1.6 CFM range.Most pumps that provide 1 CFM or less will struggle to get air to the diffuser and provide for any pump life. Also with the original depth at only 8 ft it will be necessary to turn the water several times per day to start to get the bottom cleaned up. At some point in time it would be feasible to run from 9pm to 9am if wanting to operate in that $10.00 per month range without causing problems.The Brookwood piston pump in the Vertex Air 1 would easily do this, The GAST 1.5 CFM pump (diaphram) would be pressed to do this and give any longevity.g-8-outdoors if your going to lime fertilize and feed all the more reason to aerate "properly"Taking water off the bottom will remove some of the low DO water in that area but you will still be low on DO and thermally stratified.You have to consider how will I get the warm oxygenated water on the surface to the bottm,answer > push the cooler low DO water to the surface.Look at an Vertex Air 2 and depending on the shape and average depth perhaps an Air 3.An Air 1-2-3 all have a 1/3 HP Brookwood piston pumps, I can also have units built with Gast rotary vanes if desired. If you would like a system sized fill out the online form and send me a sketch and I will do this for you.Ted