Loss of chlorine after adding scale eliminator (acrylic polymer complex)

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M

macman

0
Dec 28, 2014
9
Townsville, Queensland, Australia
I recently added a scale eliminator to our swimming pool (made up of a concentrated acrylic polymer complex) due to large amounts of scale buildup on the SWG that would quickly rebuild even after putting the cell in an acid bath.

Within 24-48 hours of doing this, the chlorine demand increased dramatically. Even with 40ppm CYA in the pool the chlorine will not hold up during the day (even with the SWG running 24/7). As a result, algae is starting to form.

The total chlorine was 0.6 and free chlorine was 0.4 at 6pm today.

This morning it was around 3ppm.

This pattern has repeated itself all week with the SWG running on full continuously.

PH and total alkalinity levels are within a normal range.

Does anyone here know what is going on, how an acrylic polymer complex actually works and (most importantly) what can be done to rectify the problem with chlorine that was induced by adding this wretched scale eliminator.
 
You need to manually add chlorine to the pool using chlorinating liquid or bleach (unscented, non outdoor or splash-less) to shock the pool by raising the FC to 16 ppm and keeping it there until the algae is gone and your overnight chlorine loss is not more than 1 ppm FC. You cannot depend on your SWG to be able to keep up with algae growth and you need to blast through the chlorine demand (regardless of its cause) by using chlorine.

What is your salt level? In the U.S. for SWG pools it's typically 3000 ppm but in Australia it's usually higher, often 5000 ppm.

Do you happen to have other products in your pool such as a clarifier? Please let us know everything you are adding or have added in the past (that would stick around, like copper-based algaecides). Usually an acrylic polymer complex will not increase chlorine demand. There are definitely metal sequestrants that will increase chlorine demand but they are typically products containing EDTA (faster chlorine demand) or HEDP (slower chlorine demand).

As for preventing scale in the SWG cell, you should not need to use a scale inhibitor for that. Instead, you keep your Calcite Saturation Index (CSI) slightly negative (around -0.2) and you use 50 ppm Borates in the water. Interestingly, with your numbers and assuming 3000 ppm salt and assuming 7.6 pH your CSI is -0.2 so I suspect that your pH may rise higher than the pool store tested or that the pool store results aren't accurate, possibly with your CH being higher than they say. It would be best if you could get your own quality test kit, though I know in Australia that can be expensive to get the TFTestkits TF-100 or the Taylor K-2006.
 
chem geek said:
You need to manually add chlorine to the pool using chlorinating liquid or bleach (unscented, non outdoor or splash-less) to shock the pool by raising the FC to 16 ppm and keeping it there until the algae is gone and your overnight chlorine loss is not more than 1 ppm FC. You cannot depend on your SWG to be able to keep up with algae growth and you need to blast through the chlorine demand (regardless of its cause) by using chlorine.

What is your salt level? In the U.S. for SWG pools it's typically 3000 ppm but in Australia it's usually higher, often 5000 ppm

Do you happen to have other products in your pool such as a clarifier? Please let us know everything you are adding or have added in the past (that would stick around, like copper-based algaecides). Usually an acrylic polymer complex will not increase chlorine demand. There are definitely metal sequestrants that will increase chlorine demand but they are typically products containing EDTA (faster chlorine demand) or HEDP (slower chlorine demand).

As for preventing scale in the SWG cell, you should not need to use a scale inhibitor for that. Instead, you keep your Calcite Saturation Index (CSI) slightly negative (around -0.2) and you use 50 ppm Borates in the water. Interestingly, with your numbers and assuming 3000 ppm salt and assuming 7.6 pH your CSI is -0.2 so I suspect that your pH may rise higher than the pool store tested or that the pool store results aren't accurate, possibly with your CH being higher than they say. It would be best if you could get your own quality test kit, though I know in Australia that can be expensive to get the TFTestkits TF-100 or the Taylor K-2006.
Click to expand...

It is a concrete pool. I actually was told by the pool shop to add a clarifying shock treatment called Clear by Softswim. It does indeed have clarifiers in it. I have also been using Softswim Clear which has minerals and I believe clarifieers as well. CSI is 0.1
 
Ahh, well using a metal sequestrant that is an acrylic polymer complex which is anionic or negatively charged at the same time as having a polymeric clarifier which is usually cationic or positively charged typically produces a cloudy precipitated mess. The more garbage you put into your pool, the more complicated and messy the chemistry is going to get. There is absolutely positively no reason for you to use hardly any of these products in your pool. Even so, I still don't know what's using up chlorine except that if it does get too low and algae starts to grow, then most SWG's can't keep up. So my advice of how to get over the hump by doing a SLAM is still relevant.

You say you get a CSI of 0.1, but how is that? If I use your numbers in PoolMath and a water Temp of 80ºF I get -0.27 so how did you get your number?
 
My guess is that something in the clarifier caused the inital chlorine demand, and that opened the door for something to get started in the pool. SLAM it to clean it out and get the chlorine under control first.

After that, you can play with the other parameters to reduce or eliminate the scaling.
 
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