Do you know the calcium hardness of your fill water? As long as your CH is somewhere around 200ppm, that’s good enough to satisfy most warranties. If your CH was below 100ppm, then you might get foaminess in your pool water since the calcium helps to breakdown foam. The foam would be caused by oils in the water from sweaty people or folks that like to apply thick layers of sunblock or tanning oils.
There is no definitive evidence that low CH causes vinyl liner problems. It is simply assumed that because vinyl liners contain some amount of calcium carbonate in them (as a mechanical filler/modifier and white colorant) that low calcium water would leach calcium from a liner and damage it. That’s simply an unproven assertion and current evidence would seem to suggest that CH is mostly irrelevant for vinyl liners.
As for heaters, that’s an argument taken out of context. Yes, in boiling water steam generators and commercial steam heating systems, the calcium hardness of the boiler water is always adjusted so that there’s a positive scaling potential and a thin surface layer of calcium carbonate is deposited to protect internal metal surfaces. This is not at all the same situation with pool water heaters but, like a lot things, the concept got borrowed and misapplied by the industry. pH is a far bigger determinant of heater corrosion than CH will ever be but the industry is stuck on having higher CH levels so there it is. Maintain your pool water CH above 200ppm and the heater manufacturers will be happy.
