Quote Originally Posted by waterbear
Calcium is what is not needed in a vinyl pool (unless it has a heater). Alkalinity is needed in all pools. It is also called carbonate hardness and is the buffer system of carbonic acid/bicarbonates/carbonates that helps to keep the pH from bouncing all over the place. Use baking soda to increase it. To decrease it see this post
http://www.poolforum.com/pf2/showthread.php?t=191
What this all means is that "total alkalinity" (which is kind of misleading) is a "stabilizer" for pH. Proper T/A will make it harder for things to influence your pH, either up or down.

People who have pH bouncing all over the place frequently have insufficient T/A. Too much is a problem as well.

So, yes, DS, you need to maintain T/A as well. Raising it is easy: You pour a bit of baking soda in your skimmer and let the filter run for a few hours.

Lowering T/A is tougher.