Hello, looks like you found a nice place. I am in the process of putting an aerator system in my pond, which also has an algae problem. I have done a lot of reading on this site and found great information.
I used google maps to outline my pond and it gave the size at .7 acre. If you use a big slip bobber with a loosely snug bobber stop and a good weight ,you can measure your depth in several spots to get a rough guess of average depth.
One aspect I considered very important was cost of operation. A fountain of adequate size will use more electricity than a bottom aerator setup and cost more upfront, at least that is the way I understand it. I chose to use bottom aerators because my pond is close to 15 foot at the deepest and you can turn the water over several times per day (to increase dissolved oxygen ) for roughly 10 to 15 dollars a month in electricity. If your pond isn't that deep you can do it for half that with a linear septic tank air pump, (good to maybe 7 foot deep)like the blue diamond et120 ( 250$). I went with a rotary vein pump for more psi and volume. I needed to push air almost 400 feet with diffuser at about 12 foot deep.
I don't mean to ramble, just trying to point out that you can put an adequate system together with a septic tank air pump that will cost less than 10$ a month to run. The idea is to turn the entire body of water over at least once per day to increase the dissolved oxygen levels which will increase the aerobic bacteria activity which will process the nutrients in the water and pond muck on the bottom which will help stop the filamentous algae and other plants from growing so fast and taking over. I am a beginner at this so you should take my info as such. This forum seems to have some really good people that love to help out.
Good luck!

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