The link Jason gave is a good starting point guideline, but how much you will use once you get to know your pool will vary a great deal from pool to pool, region to region, I am lucky enough to have fairly soft, fairly stable water that rarely needs any adjustment other than FC, so my testing schedule goes something like, test for FC every 2 or 3 days using the FAS-DPD test (I rarely use the OTO test as I prefer to have the added information), pH is tested every 2-3 weeks, the rest is every 2-3 months during swim season. This works for me because my fill water is soft (CH of around 50-60) and my pH drifts very little, I use about a quart per year of muriatic acid, by comparison someone in a high CH area like Richard where the fill water may have a CH of 300 or more, or someone that goes through gallons of acid every week will need to test pH and CH much more frequently.