The actual answer depends on many other factors, such as what other chemicals you are adding to your pool, what your various chemical levels are, if you have a waterfall or fountain, and so on. Bleach is long term PH neutral, trichlor is acidic. If your PH is constantly going up, trichlor will be closer to stable PH than bleach will. On the other hand, trichlor adds CYA, which it is not usually a good idea to be constantly adding to the pool.