You answered the questions perfectly...If you can get Alfalfa at a decent price, or one you are comfortable with, go ahead and use the best! Alfalfa has the highest nutritional valve (Sugars, proteins, etc) of any hay, and can supply a higher density of micro-organisms for a longer period.
I could find very little scientific research of aquatic uses of hay, except that it is used as a very large, super dense, feeding station...but it seems that aquarists are leading the charge and using alfalfa cubes to establish/feed beneficial bacteria and micro-organisms for a healthy tank and fry production...aquarium fry need all the micro-organisms for growth just like fry/baitfish in our lakes.
Confusing to people is the effect of certain kinds of hay to clear algae from ponds...the difference is the hay for this use has to be loosely bagged/etc, so it can decompose evenly...in this case it does not provide food and grow algae, it produces 2% hydrogen peroxide THAT KILLS ALGAE!
I think Bama will like his results...and I have plenty of chicken wire to reinforce my bales like he did!