I have a 23,400 gallon IG pool with a vinyl liner. I put one of the anchored mesh covers on the pool last fall and have encountered a new set of problems to replace the ones that I fixed with the cover. First time I have ever opened to less than perfectly clear water. I have been battling algae. I keep shocking and scrubbing but after reading assume that I haven't kept the chlorine high enough for long enough. Today I put in 5 gallons of 12.5% liquid chlorine and have been scrubbing. Here are my numbers before adding all the chlorine:

FC 1.8
TC 1.8
CC 0
pH 7.4
Hardness 40
Alkalinity 70
CYA 30

The pool store wants raise my alkalinity but from what I have read on here, I am thinking it is ok? I have already told them I am not adding calcium as I see no need for it in my pool. If I do need to raise my alkalinity, how much baking soda should I add? The pool store lady also wants to test my phosphate levels after I kill all the algae and then add a decreaser? I have never even heard of that. Since it doesn't fit the 3B's that I tend to use, I'm assuming she just wants money? What is she talking about and is that really something I need to do? I'll retest and repost in the morning. Also I seem to remember a chlorine calculator on here from a couple years ago to figure out how much to add, but I couldn't find it when I did a search. Does anyone have a link? Thanks for any help.

Lisa