Ammonia will bring the pH up, not down.

As for your second question:
I used to soak commercial fertilizer in water for a few days. It worked well on herbs. Unfortubately some of the nutrients (phosphates and sulfates) don't dissolve readily, so now I mix my own recipes from basis chemicals.

Here's a link to a fellow's Web site. His name is Daniel and he's a chemist who tinkers with hydroponics. I'm sure he'll be able to help you; he's pretty sharp.

http://allhydroponics.blogspot.com/

First of all, ammonia would increase your pH, an ammonia salt would reduce your pH. The difference is that an ammonia salt contains the ammonium ion NH4(+) which is acidic while aqueous ammonia is just NH3 (which is a base) dissolved in water.

Anyway, adding ammonia or ammonium to a nutrient solution to change pH levels is a very bad thing to do. Plants absorb nitrogen as ammonium very rapidly and this causes a very severe toxicity. Never add ammonium to your nutrient solution at levels above 30 ppm. I wrote an article about the different forms of nitrogen plants take, so you can check it out and see the effects ammonium has on plants http://allhydroponics.blogspot.com/2009/02/nitrogen-fertilization-in-hydroponics.html

By the way, thank you for the reference freemangreens !

Here is a link that might be useful: Everything Hydroponics