Caldium hardness and fiberglass pool

We had a fiberglass pool installed 6 years ago and have been slowly learning how to care for it (without being at the mercy of a pool store). The poolforum has been a HUGE help in being able to maintain it properly and understand the chemicals and the equipment.
One thing I have never fully understood is calcium hardness and having a fiberglass pool (with a chlorine generator). We were told when the pool was installed not to worry about that reading since the pool is fiberglass, but then I was told my someone at the pool store that having a SWG can be really hard on the concrete surrounding the pool and we do have to be concerned with calcium or our concrete will become pitted and corrode. I did a home reading with a test kit and confirmed it at a pool store and learned we had little to no calcium in the water, so we bought a big tub of calcium last summer and added the amount we were told to add and the reading was within acceptable levels.
So now it's a new year and I would like to understand if we really need to test for it.
Any opinions would be appreciate.

Currently I test for chlorine, ph, and alkalinity using a test kit. Ph creeps up (I lower it with muriatic acid) but alkalinity stays pretty stable and chlorine is easy to manage with the generator.