Why don’t you just pipe in seawater and make life simpler?(Just joking).
First, the warranty issue. I don’t know. You can ask the manufacturer, of course. But if they say it voids the warranty and you still want to use it, you’ve shot yourself in the foot.
Usually what I tell people is that they should install the powered anode but keep the factory one(s) because some number of tanks per year are defective. If that proved to be the case, they’d want to save the expensive powered anode but return the tank with the factory anode reinstalled because they WILL void the warranty if there is no anode in the heater.
I do not believe a heater will break because the powered anode failed to function. I’ve been selling them for five years now and I have yet to have anyone come back and say, “My heater rusted out after I bought your @#&#@!!! powered anode!”
I do seem to be the most successful distributor of the type of powered anode I sell. That said, it’s not the only one that ever was or is. Ten or 15 years ago, Familian Supply, now out of business, sold some type of powered anode kit.
Currently, A.O. Smith, one of the biggest manufacturers, has started offering powered anodes in some of their high-end heaters. You could google impressed-current anode and find they have wide applications.
If you do replace the sacrificial anodes, buy just one powered anode and plug the other two ports.
The air could be caused by overactivity of the three anodes. The powered one is less likely to cause that because it is self-regulating and will feed just enough current into the tank to protect it.