How can I safely treat algae in a 1/4 acre 12 ft deep water-table pond. I...
These nutrient issues, including things like excessive algal blooms, tend to become more problematic as ponds age. For bottom-pubble aeration to really be effective in managing nutrients, it needs to disrupt pond stratification, inducing mixing of the entire water column and making it possible for oxygen--introduced through interaction of wind and the pond's surface--to reach the substrate. That helps keep phosphorus insoluble and unavailable to fuel algae blooms. Of course, this is more likely if the diffuser is active even when the wind is still in the heat of the summer. Is it possible to get electricity to your pond to drive a more conventional compressor?
Depending upon the specifics of your site, I am skeptical regarding bacterial concoctions. There are a great many anecdotes regarding their successes, but all of those originate in the entities that make or sell them. There is a conspicuous absence of evaluations of these products in recreational ponds in the scientific literature. If you're aeration is effective, you should have some population of such things present in your substrate already.
The classic treatments for algae are formulae of copper, and if strictly used as prescribed by the label, they are safe for aquatic applications. Other treatments and methods to manage nutrients are possible depending upon the nature of your watershed. Is it possible to discuss details by phone?
In the meantime, please check this fact sheet for potentially useful information: