Stabilized VS. Unstabilized Chlorine
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Should you be using stabilized chlorine or unstabilized chlorine in your pool and what is the difference between stabilized and unstabilized chlorine anyway? The answer may shock you, pun intended, and if you choose the wrong chlorine for your pool you will probably end up with green water at some point. So let's unpack this a little bit and look at the difference between stabilized and unstabilized chlorine so you can determine which one is right for your pool.
Stabilized chlorine means chlorine that contains cyanuric acid (CYA) which is also called stabilized or pool water conditioner. The CYA content helps to prevent the UV from the sun from degrading the free chlorine in your pool. Without any stabilizer in the water then you would fail to be able to hold a chlorine level in your pool. Every day the sun would deplete all of the chlorine you have, and with rising chlorine prices I am sure you can agree that you do not want to have to use any more chlorine than necessary. So while your pool does need CYA if you only use stabilized chlorine in your pool then the CYA levels wil rise quickly to problematic levels.
How much CYA is too much? - The CYA in your swimming pool, when maintained at 30 to 50 parts per million will provide protection for your chlorine against UV. However, when the level rises above 50 parts per million the protection from the sun begins to prevent the chlorine from doing its job in the water. Unless you also raise your chlorine levels in conjunction with rising CYA levels (free chlorine equal to 5% of CYA value, minimum) then you will end up with green water. Once the CYA levels have reached 80 to 100ppm the stabilized effects on the chlorine are too strong and the normal levels of chlorine you maintain (2 to 4ppm ideally) will no longer be enough to keep the water clear. This is why it is important to maintain CYA levels within the ideal range of 30 to 50 parts per million.
How do you lower CYA levels in pool water? - A large part of the problem with using stabilized chlorine is that when the CYA levels eventually climb past the acceptable range you will have very few options to lower the CYA. Most commonly, partially draining and refilling the pool with fresh water is how you lower CYA levels. Unfortunately some pools and some geographic areas can not be drained, either due to water restrictions or hydrostatic pressure from ground water making draining the pool risky. Mobile reverse osmosis treatments are one option to lower CYA without draining. Another method which came out a few years ago are enzyme products designed to lower CYA levels, however these chemicals work only partially, and not in every situation. More recently ALUM treatments have been determined to be a viable method to lower CYA levels without draining and refilling, so while there are options there are not a ton of great options for lowering CYA once the levels climb too high.
Residuals from chlorine types - Different kinds of chlorine products will have difference residuals which build up in the water over time. Stabilized chlorine, commonly dichlor and trichlor chlorine, will add almost 1ppm CYA for every 1ppm of chlorine they add to the water. For this reason the CYA levels climb very quickly. One alternative to this would be to use cal-hypo unstabilized chlorine (pucks or granular) which does not contain chlorine. Instead of CYA residual these chlorine products will leave a calcium residual. Over time with the use of cal-hypo chlorine you will see calcium levels rising but fortunately the acceptable level of calcium in pools is much higher than the acceptable level of CYA so the calcium levels rising are a much less pressing issue than rising CYA levels from stabilized chlorine. Liquid chlorine is unstabilized also, and does not contribute to rising calcium levels, but it will add a sodium (salt) residual to the water which will also rise slowly over time. Again, the rate of which this sodium residual rises is very minor in comparison to the CYA levels rising to problematic levels with stabilized chlorine.
NEVER mix types of chlorine. You can not use unstabilized pucks in a chlorine dispenser which previously held stabilized pucks. The same goes for mixing vessels, buckets, stir sticks etc. Mixing different kinds of chlorine, even in residual amounts, can cause a volatile chemical reaction.
Some pool owners like to use stabilized chlorine products while the pool is building the CYA levels to the ideal range of 30 to 50ppm. Once the pool water reaches this CYA level you switch to an unstabilized chlorine product to ensure that the CYA does not keep climbing. It is definitely ideal to choose unstabilized chlorine for your pool to prevent from having (guaranteed) problems with CYA preventing your chlorine from working properly.
Choosing the right chlorine for your pool is important. All forms of chlorine do the same thing once they are in the pool water but the residuals from your chlorine type are what makes one option better or worse than the others. While sodium and calcium levels can rise over time from liquid chlorine or cal-hypo chlorine this will be much slower and less problematic than rising CYA levels from any stabilized chlorine source.
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