In this business we had come to accept that rain and snow always lowered the pH in all of our pools, simply because of the “acid rain” phenomenon. The last two winters and particularly last winter were exceptions to the rule. At least one, if not a number of the rains and snows last winter proved to have a very high pH, that is to say it was very basic. There are a number of opinions as to why this was, but the general consensus is that volcanic ash in the atmosphere may have caused it.
When a pool with a relatively high calcium hardness develops a high pH in cold water it can no longer hold this calcium in solution, (in a dissolved form). The calcium then becomes solid in the form of calcium carbonate crystals, ( and rarely in calcium hydroxide crystals ). These crystals typically form a loose bond with the pool wall so that when the pool is opened the walls appear crystallized. I’ve seen pools with 3 inch crystals coming off the walls. 99% of the time these will re-dissolve quickly as soon as the water warms up and the pH is balanced. The other 1% can be problematic, sometimes extremely so. When the carbonate forms a strong bond with the wall it can be difficult to treat for various reasons, but typically acidification, ( dropping the pH to 3 or so ), breaks the bond. If hydroxide crystals have formed the pool must be drained, treated directly with acid and sometimes disc sanded. It’s unclear as to why hydroxide forms.
In the past 2 winters we’ve seen this “basic rain” phenomenon begin to cause problems. We’re asking those of you who have had crystallization problems to lift your cover this winter and test the pH monthly if you find it very high we can treat it BEFORE we have any problems.
Hope your season is going well and we look forward to problem free closing season and a mild winter.
