Joe and Theo, Still plenty of DO in midwest ponds with the weather we have been having. Mother nature is mixing more than most aeration systems are designed to do so I wouldnt be in any hurry, Perhaps a month out yet unless it turns to summer next week (and it could)I have not done any DO or bottom temp checks for several weeks as I know most ponds in Ohio and Indiana are at least 80-100% saturated and probably have at least 9 ppm DO.Perhaps Cecil is more current on the readings. Joe as far as your aeration system running at 5 lbs the AQ7 (3/4hp Gast) creates 9.5 cfm at that pressure,(8.8 @ 10 psi) If you have that much cfm going to one diffuser it should be boiling "big time" If you have the 4 stone setup per diffuser (ALA4GL the cfm range is 1.5 to 2.4 each and the ALA6GL is 3-7 cfm with 6 stones per diffuser)In order to keep your pressure as low as possible (which you want to do) be sure those stones are removed yearly for cleaning per the AES Sweetwater instructions. If you dont have the instructions I have them posted under "A word about diffusers" on my home page, also when you have them out if there is a 3/4 inch blue "Brady" checkvalve where the tubing connects unscrew it apart and remove the spring and the pump will have to work a little less. AES started removing those springs a few years ago but I still find many systems and diffusers with them in.As far as replacing your pump it is not needed as just making some minor changes may be the only thing needed, you have plenty of pump for a 2.5 acre pond.Let me know if you have the ALA 4 or 6 and check into the check valve issue. While your at it and have the checkvalves apart see if the o rings are cracked as they usually are after a year or two.If your Sweetwater does not have the two end caps filters and most Sweetwater units do not, consider the dust from the sacrificial rotary vanes are probably collecting on the inside of the stones thus one of the reasons to clean them yearly.Lastly I would put the one diffuser in 20 ft of water and watch the pressure guage and slide it deeper until the guage is just under 10psi, putting it just under 10 psi will give you room for 10% additional backpressure as the stones slowly get material either in them or on them prior to the next cleaning.Also if you have a liquid filled pressure guage be sure it is "vented" at the rubber fill plug on the top as these guages are normally shipped unvented and will read pressure without venting but not accurate.Good Luck Ted