Silver,Good question. Depends on the capability of the diffuser and not the total number of diffusers in your case for a small pond. If you know how many times you want to turn your water over per day (perhaps twice)and you know that you have for example approx 2 million gallon of water the next step would be to know what the turnover rates are at given depth at given cfm's.If a certain diffuser will circulate for example 2778 GPM at 1 cfm in 12 ft of water it will turn 4 million gallon per day. This diffuser and pump setup would have the capacity to turn your pond over twice per day or if less turnover wanted run less hours per day or simply slow it down..If you wanted the same turnover but had a shallow area or beach area that you wanted to keep a higher DO level or use as a winter optional diffuser then add a second diffuser in that area off of the same pump.If cool water or cold water fish a concern then slow the circulation down when hot and speed up in spring and fall.If you use the barometer of live fish dead fish as to if a pond is properly aerated or not chances are most any diffuser will work. If you want to maintain a high percentage of DO and maximize on aerobic bacteria and create a great enviroment for aquatic organismns then research what diffusers will do this and which ones wont,Try to size a system for what you want to do with your pond. Same pond a mile down the road may need a slightly different system Good Luck Ted