Total alkalinity is the most important thing (whether your pool is using chlorine, salt or bromine).  It's what allows the chlorine to work or not, (how much you will need), whether the pH is constantly at 6.8, whether the algaecide can do its job and control algae, whether your heater is protected against acidic water what eats through everything and let's not forget the bather's comfort and your wallet.

Since the total alkalinity level goes down slowly, changes faster with rain, bathers, it needs to be readjusted at least once a month. Otherwise you will need lots of pH+, (unless your using a high pH chlorine sold anywhere, or a salt pool which produces a high pH level chlorine), more chlorine, more shocks, so, more money and less chances of enjoying your pool.

• The ideal level for a vinyl liner pool: 125 - 150 ppm
• The ideal level for a fiberglass pool: 125 - 150 ppm
• The ideal level for a cement/concrete pool: 80 - 125 ppm
• The ideal level for a salt pool:  100 - 125 ppm
• A level of total alkalinity too high and you end up with scale.

The quantity of the product to be added depends on its concentration, the quantity of water and the actual level of alkalinity upon water analysis.

After a party or a few days of rain, an adjustment should be done. 

So, total alkalinity is the 1st thing to be balanced, then the pH (since total alkalinity changes the pH).