Re: Calcium for metal
Actually, we run our pool, which is solar heated most of the time (for 5 months and gas heated about two months a year), at 88F since my wife uses the pool for swim therapy and I've always liked the warmer water temperature (I'm still pretty skinny).Originally Posted by RavenNS
The best research on corrosion that I can find shows a rough doubling in corrosion rates for each 10C (18F) rise in temperature. The temperature inside a gas heater could be, near the metal surface, up to 30F higher so that is the most likely place for a problem (if any) but typically it isn't corrosion that people are worried about (since they keep their pH well above 7.0) but rather scaling since the higher temperature (ironically) makes it more likely to precipitate or scale calcium carbonate. So in plaster/grout pools, some people (Ben, for example) keep their pools on the slightly corrosive side so that the higher gas heater temperatures don't cause scaling. However, I've been educated on this forum by how extreme the water balance must get before either corrosion or scaling of plaster starts to occur (the LSI or equivalent index seems to tolerate even 1.0 without problems rather than the "official" 0.3 or 0.5 limit) so I really don't have a good answer except that we (including myself) probably worry about this too much.
So if I were you, I wouldn't worry about corrosion or scaling and just keep you pH well into the normal range above 7.0. As far as temperature goes, spas are typically at 104F and I don't know if anyone adds calcium to spas nor have I heard of corrosion problems in spas that are not due to low pH. Of course, the relatively low volume of water in a spa compared to the relatively large number of people who can use a spa makes maintaining pH balance a real headache! Again, if anyone has any contradictory experience, I'd like to hear about it.
Richard
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