It is difficult to maintain a pond as a clear water swimming pool. I have several ponds used mostly for swimming and domestic water use near me that have water visibilities that commonly range from 8ft to 18ft. IMO one of the biggest problems will be the muck and dead organics accumulation on, in, and among the gravel bottom, sand or sediments.
Firstly I don't think you can decrease the pH and maintain it consistently low for long periods, at least a pH too low for fish survival.
Secondly TJ is correct: "No fish = mosquitos and lots of biting backswimmers/water boatmen". Mosquitos can be pretty well controlled by dragon fly larvae and adults, but water boatmen and back swimmers are another story. I've seen water boatmen and backswimmers as dense as 1 per quart of water in fishless ponds. Supposedly the water boatmen do not bite but both have piercing mouth parts. Whirligig beetles on the surface can make some swimmers shy to enter the water. They can bite if handled.
http://beneficialbugs.org/bugs/Whirligig_Beetle/Whirligig.htm My recommendation for smaller (0.1-0.5ac) swimming ponds has always been to add a few smallmouth (SMB)or largemouth bass(LMB) (10-30) and forget about any other fish. I prefer SMB because they thrive better on a mostly 'bug' diet. The bass: A. will not get big (7"-9" maybe10"), B. will not bite swimmers, C. do not need to be fed, and will keep the bugs, crayfish, tadpoles, and small critters controlled. The adult bass (8"-10") do not eat the larger zooplankton, mostly Daphnia, which will keep the water generally clear unless the pond gets an excess of nutrients from watershed, leaves, waterfowl or feeding fish.
Pictures of your pond project show trees fairly close to the pond - a big concern for me because of annual tree leaf inputs which introduce organic materials that make muck and dissolved nutrients which grow algae. Tree leaves are a big problem for pools and ponds. Pool owners skim leaves and large organics daily. Algae as phytoplankton or filamentous will be low or sparse as long as you can keep nutrients and organic inputs at a low concentrations. If the pond water has low alkalinity this will also help keep algae less. Secrets to keeping clear water in a pond are low nutrient concentrations and some rooted vegetation to utilize what nutrients are present. You will probably always see a little bit of filamentous algae. Large amounts indicate way too many nutrients. Although large amounts of filamentous algae generally causes clear water conditions due to binding lots of nutrients and starving phytoplankton. Harvesting some plants each year helps keep the nutrient budget low. The more plants including algae that you can harvest each year the less the filamentous algae that will grow. Filamentous algae only grows on the excess dissolved nutrients not utilized by other plants (phytoplankton and or rooted).
Bottom diffused aeration helps keep the water clearer, fresher and helps speed the decomposition of organic materials such as dead plants on the bottom. In NH proper sized aeration will not need to run 24/7 to keep the pond in good balance with clear water as long as you provide 1 to 2 turnovers per day in a small pond which could take 4-6hrs.
