Confusing Chlorine Tests

[stvt]

Hi, everyone. I’m new to managing my pool and could use some guidance.

Initially, I used test strips, which showed chlorine levels off the charts. In response, I turned off the SWG and added water, but after more than two weeks, the chlorine still tested very high.

After reading recommendations on this site, I purchased the TF test kit.

The block test showed an extremely bright yellow, not matching any of the reference shades.

However, the chlorine drop test showed 5.5 ppm free chlorine, 6 total chlorine, which doesn’t seem excessively high.

My CYA was very low. The dot never disappeared, so I added the amount recommended by pool math.

I turned the SWG back on to 10%.

What am I misunderstanding or doing wrong? Any advice would be greatly appreciated.

Thanks in advance!

 

[sande005]

Welcome to TFP! You found the best place to be.

Sounds like you did everything correctly. Nice job on learning from this site!

The block test tops out at a reading of 5, so generally is just a quick "Do I have chlorine at all?" type test. Most of us rarely use it. The powder and drop testing is the definitive.

What is your Combined Chlorine? .5 or less?

Is the CYA of 30 the current, or the previous "very low"? While TFP recommendations are for a CYA of 60 for a salt pool, staying at 30 is not a big issue - IF you make sure to always keep the CL at the top of the recommended range (6+). You can go all the way to the SLAM level, and swim safely. But that high would put use on the SWCG that isn't needed. Going to CYA of 60 (and the related higher CL level) will give a bit more margin for unplanned events - pool parties, storms, etc. CYA can be slow to dissolve, so take a few days between adds and testing, to make sure. It is the hardest test to get a repeatable reading from.

Our standard chart is below, which Pool Math also uses to base it's recommendations.

Your pH is fine, but will rise over several days, requiring acid to drop it back into the 7's. This is due to the TA being 90. Over time, the acid adds will slowly drop the TA too. Once 70 or below, the pool will get more stable with pH, and require less acid, less frequently. Use hardware store muriatic acid, not pool store "dry acid", which can damage SWCG cells.

Your salt level is pretty high. Jandy recommends 3000-3500. Surprising your SWCG isn't throwing an error. Consider replacing some water to bring it down. Or do a rain dance.

You can link pool math to the same username/password here (in the gear/setup section of Pool Math) so you don't have to post screen shots. Click on my user name and see my Pool Math logs (it's winter, so they are pretty old!)

 

[stvt]

Welcome to TFP! You found the best place to be.

Sounds like you did everything correctly. Nice job on learning from this site!

The block test tops out at a reading of 5, so generally is just a quick "Do I have chlorine at all?" type test. Most of us rarely use it. The powder and drop testing is the definitive.

What is your Combined Chlorine? .5 or less?

Is the CYA of 30 the current, or the previous "very low"? While TFP recommendations are for a CYA of 60 for a salt pool, staying at 30 is not a big issue - IF you make sure to always keep the CL at the top of the recommended range (6+). You can go all the way to the SLAM level, and swim safely. But that high would put use on the SWCG that isn't needed. Going to CYA of 60 (and the related higher CL level) will give a bit more margin for unplanned events - pool parties, storms, etc. CYA can be slow to dissolve, so take a few days between adds and testing, to make sure. It is the hardest test to get a repeatable reading from.

Our standard chart is below, which Pool Math also uses to base it's recommendations.

Your pH is fine, but will rise over several days, requiring acid to drop it back into the 7's. This is due to the TA being 90. Over time, the acid adds will slowly drop the TA too. Once 70 or below, the pool will get more stable with pH, and require less acid, less frequently. Use hardware store muriatic acid, not pool store "dry acid", which can damage SWCG cells.

Your salt level is pretty high. Jandy recommends 3000-3500. Surprising your SWCG isn't throwing an error. Consider replacing some water to bring it down. Or do a rain dance.

You can link pool math to the same username/password here (in the gear/setup section of Pool Math) so you don't have to post screen shots. Click on my user name and see my Pool Math logs (it's winter, so they are pretty old!)

View attachment 626663

Thank you so much for your detailed and thoughtful response.

The combined chlorine level is 0.5. The CYA was around 30 before I added more, but I haven’t retested yet. The dot on the test never fully disappeared, though it was mostly obscured near the 30 mark, so the actual value may be lower. It was my first time doing the test so it was a bit of a crapshoot. I added the full recommended 74 oz of the stabilizer, but next time, I’ll follow your advice and add it gradually over a few days.

The Jandy initially indicated that the salt level was too low. I added one 40 lb bag and waited, but the error persisted, so I added another. The error is now cleared, but the salt level is above the recommended range. I’ll retest in a few days and adjust by adding more water as you suggested. I’ll also add muriatic acid in a few days.

We never use the pool, but I have a young baby with very sensitive skin, so I’m especially concerned about keeping the chlorine levels from being too high.

 

[sande005]

There's a lot more detail, and much deeper rational and chemistry to back it all up on this site...but at a high level:

Don't make the error of running at the min. Cl level, to be gentler on sensitive skin. It is generally the by products of "killing things" that cause many of the skin issues - chloramines and the like. The hallmark of a dirty pool is one with a strong "chlorine" smell. Running at the minimum greatly risks algae and other growing things, which produces the by products. The test for this is the "CC" or "Combined Chloramines" test. 0 to .5 is best, higher and you have issues with something growing.
CYA absorbs a lot (95%) of the chlorine that is added to the pool. As the remaining active Cl is used up (organics, sunlight, etc.) , some of that bound to the CYA is released to maintain equilibrium. While not a strong reserve, it does help smooth fluctuation. With a salt system, since they are slowish to replace losses, we run higher in CYA to give a bit more buffering.
Our tests are only able to measure the total Cl in the pool - both active and bound to CYA. Few of us could afford the lab equipment to test just for the active Cl. While the levels recommended seem high, to very high, from standard pool store recommendations, they are based on keeping the active amount appropriate, while recognizing that most of it is bound up in CYA.