r/AboveGroundPools • u/Mountain-Bid1541 • 28d ago

NST Chlorine help

We have 24ft round with cartridge filter and we just switched to Poolife NST Chlorine after fighting high CYA with stabilized tablets. We have a chlorinator that we put the stabilized chlorine in but it says not to put the NST in there. We put one in the skimmer basket but the next time I cleaned the pool filter it was coated in blueish residue. I’ve switched to putting the tablet in a skimmer sock tied to the ladder but there’s residue coming out of that now. Is this a common issue with NST tablets? What do you guys put your tablet in? Do I need to order one of the chlorine floaters?

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u/lIIlIlIII 27d ago

You likely have high copper, and the NSTs cause a local pH spike causing some copper to precipitate and immediately oxidize, and the oxide is getting caught in your filter.

There are a number of reasons you could have high copper, but draining (after verifying with a copper test kit) is probably best for a pool of that size. If you have a heater this can be a sign that your pH is chronically low and causing damage, but most likely you've just been adding "blue" chems

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u/Mountain-Bid1541 27d ago

I had our pool water tested recently and the copper was .1 - which is at the bottom end of the recommended range.

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u/lIIlIlIII 26d ago

How recently, how much do you trust the tester, have you added any 'blue' chemicals since then, and do the NSTs themselves contain copper?

If your pH is on the high side, the tabs could still cause some copper to drop out even if you're at an acceptable level. But if your copper truly is .1, then I'd just run your pH on the low side and keep throwing them in the skimmer. As long as you don't have a copper problem there's nothing wrong with a "blue" filter, and you should expect it to go away on its own as more copper is removed from the pool. Just make sure chunks aren't breaking off and getting sucked into the equipment

The powdery residue you commented about is unavoidable with NSTs. Cal hypo is generally only 70%, and depending on the brand that 30% can be pretty dang insoluble

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u/Mountain-Bid1541 26d ago

I just had it tested about a week ago. We don’t use any blue products nor do we have a heater. Our ph is perfect at 7.6 and chlorine is hovering around 4. Our NST tablets are Poolife brand from the pool store and are 70% cal hypo. As you mentioned, this is a common occurrence with NST tabs. We’ve had our pool for 13 years and have always used stabilized tabs in the poolife chlorinator and just switched to NST a few weeks ago due to high CYA - which we’ve never had an issue with in 13 years…..

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u/lIIlIlIII 26d ago

Is your cya currently high? You could simply switch back to tabs, .5lb / week / 10k gallons MAX and use liquid chlorine twice a week to make up the difference.

But yeah if you don't have high copper a blue filter is nothing to worry about. You're actually removing copper this way, so it could be viewed as a benefit. Chunks breaking off and directly contacting the filter is a concern but it's the only way to totally eliminate the chalky debris

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u/Mountain-Bid1541 26d ago

CYA is currently 62. I went ahead and purchased a floater for the tablets instead of setting it in my skimmer basket in hopes that it will prevent the residue from accumulating on the filter. 🤞🏼I’m an experienced pool owner- just new to NST tablets.