Low ALK.

Hi everyone! Seems that the last week of hard rain showers has lowered my TA.(Is that possible??) Last year was our first year with a pool and I found this site only a couple weeks after installiation which has already save me $$$.
I just checked all my readings last week before the rains and all seemed ok and water was Crystal clear but here were my readings before..

FC: 8
CC: 0
TC: 8
PH: 7.8
ALK: 120
CYA: 60
TEMP: 82

After the rains my water became cloudy and I just added a gal of bleach that night and one gal the next morning my now my readings are

FC: 15
CC: 0
TC: 15
PH: 7.8
ALK 50
CYA: 60
TEMP: 84

What would have happened to my ALK? I am still new at this and read often here to learn but never noticed alk drop like this.

Once I started using the bleach method that everyone here seems to use all my levels have stayed constant and has been great. I did add 8lbs. of borax already (hope thats right) but just curious if this is common to happen after a couple days of hard rain showers. Also after the rain I have to sweep the bottom of the pool because I have stuff all over it. Me and the wife were discussing this and don't remember any of these problems last year after a rain or ever having cloudy water.
Thanks for any help or answers you guys can give me. BTW what Does the BBB method mean?? I see this on the forum all the time.

Ok, I added the borax when I should have added baking soda. My ph is off the chart this morning. My ph was fine at about 7.8 yesterday and I grabbed the wrong boxes and put 8#'s of borax in my pool. How much muratic acid do I need to put in to bring this down to where it needs to be? And what effects will this have on my pool. I am leaving out of town today for a week and I guess I better get this taken care of before I go?
Hope someone sees this quick, I need help.
Thanks
Also when will it be ok to add the baking soda to raise my alk?

Somewhere in the neighborhood of 1/2 gallon of muriatic acid should neutralize the pH increase of 8 lbs of borax. I would start with a pint and keep adding a pint at a time and restesting until the pH is in range....then add your baking soda to rasie the TA and then retest the pH and adjust. You need to do this over a few days time. Don't try and do it all at once!

And yes, rain can lower the TA!