RB:
You need to do some reading. Go to our various forums and read the stickied threads we placed there. They will help you.

Also (ASAP) go to PoolSolutions.com and read ALL the tips there. They will give you a great headstart and aren't hard to follow.

The problem with most information we get from pool stores and pool companies is that it just doesn't make any sense. With your stabilizer (CYA) level of 120, you MUST keep your chlorine between 8 and 15 parts per million or you WILL get algae. With it that high you shock by raising chlorine to 25ppm. The maintenance and shock levels vary depending on the CYA level

That's why we have the "Best Guess Table" to show you.

To lower Alkalinity, there's only really one way.

Here's what I wrote on another thread:

There's really only one way, short of dilution with low T/A water to lower T/A and that's what's here. It's not always clear so here's how you do it:

1) Lower pH to 7.0-7.2. (Muriatic or dry acid are both fine) This lowers T/A somewhat.

2) Aerate your water. This raises pH WITHOUT raising T/A--and it's the ONLY WAY TO DO IT!

3) Lower your pH again to 7.0-7.2, bringing T/A down some more.

4) Aerate to raise pH again without raising T/A.

5) Repeat until T/A is in the desired range.

You "ratchet" your T/A down. T/A and pH are linked. pH goes up, T/A goes up. pH goes down, T/A goes down. ONLY BY AERATION can you break that cycle and do the raising of the pH without raising T/A, allowing you to lower it more the next cycle.
Here's the link:
http://www.poolforum.com/pf2/showthread.php?t=7561

That forum has a lot on lowering T/A.