Low calcium hardness in vinyl pool ok?

[chem geek]

There's a lot of discussion among the experts on whether calcium carbonate saturation helps to prevent metal corrosion and you can read just one such discussion here:

http://corrosion-doctors.org/Cooling...orrosivity.htm

The bottom line is that it is pH that is a critical factor in corrosion and next would be a low TA since that would allow for a low pH locally when there is no water flow. The presence of chlorides, sulfates and generally the conductivity of the water are also important. Of course, one must have an oxidizer in the water as well such as dissolved oxygen or, of course, in pools we have chlorine. Calcium carbonate saturation is iffy at best since getting a consistent protective patina is quite difficult to achieve. If calcium directly interfered with the corrosion process, then that would be different, but there is no evidence that this is the case.

Many people have copper plumbing in their homes and have either chlorine or monochoramine in their water systems yet the water is often very low in CH (50 ppm or lower). Water districts often add some corrosion inhibitors, but they don't saturate the water with calcium carbonate. Also, there is no CYA in tap water so any chlorine is far, far higher in active concentration than found in pools. Pools with an FC that is at or above the minimum in Ben's Best Guess CYA chart (an FC that is 7.5% of the CYA level) are equivalent in active chlorine concentration to water with only 0.06 ppm FC with no CYA.