Free Chlorine Testing

[shclayto]

Hello,
I have discovered a major difference in my Taylor k-2006 free chlorine test results when compared to numerous other methods. Two days ago, the Taylor kit measured 8.5 but algae had once again started to grow. I took a water sample to two pool stores. Each store tested using their digital kit and test strips. Their measurements varied between 2.5 and 4.5. I then remeasured and again got 8.5. The algae continued to grow (slowly) so I shocked and brushed yesterday. I then retested FC today and got 17 (tested two times). I also took a sample to same two stores and received results from 6-9. I am now concerned that my chlorine has been lower than I expected which could explain why I had an algae bloom while out of town about three weeks ago. I have been using 3-inch chlorine tablets this summer.

Any idea what is going on with my kit? I should also say that I have a new bottle of reagent. My numbers from two days ago are below. They have been fairly consistent all summer. Any help would be appreciated. Thank you.

FC - 8.5
CC - 0
PH - 7.5
TA - 120
CH - 130
CYA - 50

 

[duraleigh]

Welcome to the forum.

You may not like the directness of this answer but it is not intended to offend.

When you got your pool store test for free, you received results worth exactly what you paid for them.

Now, your test results...

You have tested 2 or three times (that's not clear to me) and you got 8.5 each time. In between you tested and got 17 ppm

Chlorine cannot increase in your pool unless you put it in. To double your chlorine without adding any is simply not possible.

Have you reviewed your procedures and checked for a math error? (8.5 x 2 =17...is that a possibility?)

A tenant we teach here is trust your own testing. Pool Store testing is notoriously inaccurate and I would suggest you stay away from pool stores if you are going to take charge of your own pool and manage it. Nobody at the pool store cares about your pool as much as you do and their semi-impressive testing equipment can't hold a candle to the kit in your possession.

 

[shclayto]

Two days ago, I tested FC two times and both readings were 8.5. The next day I noticed algae starting to grow on the bottom of the pool so I added two pounds of cal-hypo shock. That's how the FC increased. I retested today two different times and read 17 both times. I trusted my k-2006 results until algae starting growing when my FC hasn't dropped below 6.0 in the past month. That's what made me second guess the results. If my measurements are accurate, how is it possible for algae to reappear every 3-5 days? Thank you for the input.

 

[duraleigh]

When you have visible algae, you must SLAM the pool, not just add chlorine. SLAM is a combination of chlorine and filtration and brushing and vacuuming that, IF you do it according to the SLAM article in Pool School, will result in your pool being crystal clear.

The algae will not return unless you allow the chlorine to fall below the levels suggested in Pool School.

 

[Isaac-1]

Ok, let us review how your doing the test, are you using the 10 ml sample and adding 1 scoop of 870 powder, and having each drop count for .5 ppm, so a reading of 8.5 ppm FC was a count of 17 drops of R-871

 

[shclayto]

Yes I am using the 10 ml line and dividing number of drops by two just as you described. I have been using two flat (not heaped) scoops of powder as per the instructions. So my most recent reading of 17 ppm was 34 drops.

 

[BoDarville]

Here's a textbook example of why we do not recommend pool store testing: Inconsistency in readings.

 

[spidey07]

Are you dropping R-871 about once per second? You want nice full drops that hang on the tip for a bit before falling. If you force them out quickly you could have smaller drops leading to higher than actual results.

 

[DorsalSpine]

I have watched my pool store test my water. It looked really impressive with the computer printout and the detailed instructions. My rose colored glasses came off when I paid more attention to the testing and less to the printout. They were using strips and a standard color block test for FC that maxes out at 5ppm.

The kits recommended here were better than anything they were using. The real deal breaker is when I asked them to double check my CYA. They told me it was 100 but they would help me "manage" that. I knew perfectly well it was 2 or 3 times that based on my testing. I was new to testing and wanted some reassurance. That was my last trip to that store.

Trust your numbers and double check your assumptions. It sounds like your testing is correct. The shock you added should have raised your FC from 8 to 17 per the pool calculator which validates your test. The only other thing is your CYA level. Are you sure it is 50?

If you CYA is much higher, your FC may be borderline which would explain your algae problem. The algae is why you are questioning your test results.

 

[Isaac-1]

If you want a sanity check get a cheap OTO color matching (shades of yellow, not DPD shades of pink) chlorine test and see if the color is in the right ballpark. OTO may not be the best for precision, but it is great for a sanity check.

Ike

 

[gtemkin]

Just throwing this out as a slim possibility. You mentioned in your 1st post that you used a new bottle of reagent. Have you checked that it's the identical reagent to the kind originally supplied with the kit? Sometimes the Reagent part numbers are so dislexicly (made up word) similar to one another, it's easy to make an error.

 

[kendjelic]

Ok, let us review how your doing the test, are you using the 10 ml sample and adding 1 scoop of 870 powder, and having each drop count for .5 ppm, so a reading of 8.5 ppm FC was a count of 17 drops of R-871

I currently use what you suggest above except two scoops of 870 which is the same as the OP as well. Should we only be using one scoop when testing only 10ml?

 

[scott.MI]

When you have visible algae, you must SLAM the pool, not just add chlorine. SLAM is a combination of chlorine and filtration and brushing and vacuuming that, IF you do it according to the SLAM article in Pool School, will result in your pool being crystal clear.

The algae will not return unless you allow the chlorine to fall below the levels suggested in Pool School.

Should start with that as your first step. Follow the SLAM procedure until you pass the 3 goals, especially the OCLT, then maintain your regular FC and see what how that works.

If my measurements are accurate, how is it possible for algae to reappear every 3-5 days?

Have you followed the SLAM procedure yet or done an OCLT before? That's the great thing about the SLAM and OCLT, there is no "well It looks good and I don't see anything I think the algae is gone". Until you pass your not done.

http://www.troublefreepool.com/pool-school/shocking_your_pool

 

[scott.MI]

Each store tested using their digital kit and test strips. Their measurements varied between 2.5 and 4.5.

each pool store tested FC twice? or 1 store tested with digital and the other tested with strips?

The way I see it from a range of 2.5 and 4.5 that's a different of 2ppm or 45%... A range of 6-9 is a difference of 3ppm or 33%. That's a large margin of error between them and doesn't comfort me as to their accuracy.

As said above, should trust your testing/readings, follow the slam process and keep us updated.

 

[shclayto]

Thanks for the feedback. I performed the OCLT and chlorine did not drop over night. For the past week, everything has been as expected with crystal clear water. I am now convinced that my measurements are accurate and the "algae" on the floor was fine debris that the filter has not captured. After about two days, the same amount of debris appears in the same places...creases and wrinkles of liner. I will get it vacuumed out and think I am good to go. Thanks again for the input.

 

[spidey07]

Thanks for the feedback. I performed the OCLT and chlorine did not drop over night. For the past week, everything has been as expected with crystal clear water. I am now convinced that my measurements are accurate and the "algae" on the floor was fine debris that the filter has not captured. After about two days, the same amount of debris appears in the same places...creases and wrinkles of liner. I will get it vacuumed out and think I am good to go. Thanks again for the input.

Cornerstone of troublefree is trust your own results and testing with your quality test kit and nobody else. Your testing is to be trusted.

What you describe is just low flow in certain areas and to be expected or the wrinkles/seams "catching" stuff. Brush it weekly or adjust your returns to achieve better flow. You'll never get it perfect and will need to vacuum from time to time. That's dirt/dust/pollen that collects in the crevices.

Your OCLT confirms your pool is clean and sanitized.