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Is there some explanation as to why in the 10 years I have owned my pool, the previous 9 years' openning regimen was very simple. I was able to use very little chlorine to shock the pool and I was in business. This year, I had the ammonia problem from CYA broken down into amonnia which required enormous amounts of chlorine to break.
Is there something I can do in the fall when closing my pool to help avoid this problem again?
Who knows why it happened. There really is no way to keep it from happening that I know of. Make sure you close as late as you can in the fall with high chlorine and open as early as you can in the spring. But, even that is no guarantee.
It's going on all over this spring. I suspect the warm winter with less freezing is the culprit. I did not have that problem though, but part of that was I lowered my water far lower than usual to take care of some maintenance--new light housings, new returns, and a patch 2 feet up from the shallow end. So I added just enough water to start the pump running with the low drain, and with the skimmer shut off, hammered it with LC, vacuumed and brushed and refilled--and have been fine. But my CYA was gone, too.
We know that bacteria can convert CYA into ammonia and sometimes, fortunately, to nitrogen gas, carbon dioxide, and nitrate (see Degradation of Cyanuric Acid (CYA) for technical details). The former conversion requires a LOT of chlorine upon opening to get rid of the ammonia while the latter does not. Both show up as a loss of CYA.
Unfortunately, we haven't figured out a way to control this, especially the latter conversion since that would be a fantastic way of lowering the CYA level in pools. The previous posts give good recommendations for minimizing the chances of this occurring. By closing as late as possible so that the water is cold and opening as early as possible, this minimizes the chances of having the bacteria grow enough to do the conversion, but they can still grow (this approach is better for minimizing algae growth since they grow more slowly to begin with). If you were able to maintain a chlorine level over the winter, then that is the best approach, but for freezing climates that isn't practical.
Chem geek- is it safe to add bleach during winter with the cover on, and pump off? Just wondering... I am already trying to get a game plan for fall/winter, so I can avoid the headache I dealt w/ this spring
Good question and my gut feel is no, it's not a good idea unless you find some way to mix the water even if you don't do it using the regular pump. Perhaps using some sort of submersible pump temporarily after adding the chlorine might mix it up somewhat if the pool is small and you point the outlet hose in a way that tends to swirl the water (especially for a round pool).
Closing late and opening early is probably your best bet. Some people close with a strong dose of Polyquat 60 in addition to chlorine. If the water is cold enough, the Polyquat will last quite a while. Even chlorine will last if not exposed to sunlight. In my own pool with a mostly opaque cover and with the water at 50ºF during the winter, my daily chlorine loss is around 0.1 ppm FC, but I'm able to maintain the chlorine level adding some every couple of weeks.
Richard's right. I close by waiting till the water is 60 deg or less (if practical), shocking my pool up to the CYA shock level, adding 1 quart of Polyquat, waiting 48 hours (Polyquat drops FC levels), bringing it back up to shock level, and closing. I use a safety mesh cover. If we have a good, cold winter I'll get a foot of ice on the pool. By mid-April, when the ice melts, if I open then, I usually do NOT have algae. I've only had algae the last two openings--because I opened late last year and this winter was warm. But it was cleaned up very quickly because I don't hesitate to hammer it with LC, usually in 24 hours.