Why is low alkalinity a problem? I run my alkalinity around 50 and keep pH around 7.5. I only have to adjust pH every 2 weeks. When I use to run higher alkalinity I had bad pH problems.
Jim,

Alk around 80-120 is a nice general range. It can best be described as a buffer to prevent pH from moving too quickly. I don't doubt your success at 50, but for most pools, I would consider that a little too low.