If you have too much cynaruic acid do you need to drain the pool?

Answer 1

I usually tell my customers to watch the pool, keep the chemicals balanced, and if it stays clear, then the chlorine is not being blocked out by the stabilizer. If it turns green and the chlorine level is normal, then the chlorine is being blocked out, and the pool needs a couple of feet of water drained off. Whatevever you do, don't use any more chlorine tablets until the stabilizer is back to normal, only use liquid or granular chlorine. The tablets put stabilizer into the water and should not be used during the winter to prevent the stabiler level from becoming too high.

Yes you must drain part of your pool when the cyanuric acid exceeds 100 ppm. Almost every health department in the nation abides by this. However, this is depated in the pool industry, even amongst my own employees. It is thought that the cyanuric acid molecule locks up the chlorine molecule when you exceed 100 ppm. Thus, you have a greater chance of the pool clouding, bacteria/virus build up etc.

To get your Cyanuric Acid (CYA) level down to the recommended ideal of 40 ppm from your 100 ppm, you would have to drain 60% of your pool water and refill with tap water (which has no CYA). Be careful about draining your pool since doing so in areas with a high water table can damge your pool. Instead, you can do "continuous" draining where you simultaneously drain (with a pump or spillover) and fill your pool (filling from one end and draining from the other, all with the pump running for decent mixing). This will take longer and use more water, however (about 150% of your pool volume).

One thing that most pool companies won't tell you is how much CYA you add to your pool by using Tri-Chlor tablets or Di-Chlor granules. One 3" tablet of Tri-Chlor provides around 2.5 ppm of chlorine, but also 2 ppm of CYA. The same amount of chlorine is provided by around 13 oz. (weight) of Di-Chlor, but this adds 3 ppm of CYA or 1.5 times as much as with Tri-Chlor. With chlorine demand of around 0.5 per day, you can easily see how you can build up an excess of CYA (about 12 ppm per month) over just one summer!

If you use a DE filter that requires regular backwashing or if you have a lot of splash out, then you will always be diluting your CYA and might prevent too much build up, but if you use a cartridge (fiber) filter and don't backwash, then you will build up too much CYA.

I had this same problem and am using winter rains to help dilute my pool and have switched to using liquid chlorine. This sure is a good argument for using a salt pool or liquid chlorine instead of Tri-Chlor!

Answer 2

CYA attains over 85% effectiveness for retention of free Chlorine at only 20ppm. That is essentially the point of diminishing return for CYA as far as retention goes. And it causes harm by reducing Chlorine's sanitizing power as you go higher and higher. At 70ppm CYA, no matter how much Chlorine you add, the killing power will only be as effective as 0.2ppm of free Chlorine. This is dangerous! You should do a partial drain and refill to get CYA well below 50ppm and keep it below that.

The pool store guys are usually clueless about this. And it helps them sell other products (algaecides and the like). The Chlorine tabs they sell to you will continuously increase CYA. Once you get the CYA down to below 50ppm, switch to liquid Chlorine. About half the price of the pool stores at Home Depot.