Slamming required 33 Gallons of Liquid Chlorine in 24hrs.

[rotortool]

I processed my first SLAM and would like to know if someone could explain what might have happened that would have caused me to use 33 gallons of liquid chlorine.

Situation:

• Pool – 36,000 gallons
• Located in wooded area and algae is a chronic issue we deal with
• Temp – 55 and no sun
• All test performed using Taylor Test Kit (K-2006).
• Pump flow is 49.5 GPM (Metered)/ 12 hours = 36,000 gallons.
• Sand Filter.
• Pump did not turn off except for backwashing.
• All Chlorine was applied evenly by circling the pool, one arm length away.

Water Quality Prior to testing

• CYA – 30 (also tested by pool supply stating 38)
• PH – 7.4
• CH – 90

Prior to SLAM I Purchased 16 gallons of LC (10%) from local pool supply, which they asked me three times if I was sure that was the correct amount! As instructed, I vacuumed pool to remove heavy debris.

So I began the SLAM in the morning with a commitment to maintain a FC shock level of 15 but I didn’t imagine I would go through 31 gallons. Based on my pool volume, 1 gal LC(10%) will generate 2 ppm so I planned to start with 8 gallons of LC.

Timeline:

• Add 8 gal of LC (10%), test after 30 mins FC = 8.2
• Add 4 gal (12 total) of LC (10%), test after 30 mins FC = 8.8
• Add 5 gal (17) of LC (10%), test after 30 mins FC = 8.8
• Ran to local grocery store for 8 gallons of bleach (8.25%)
• Tested 60 mins since last test, FC = 9.6.
• Sent wife to different pool supply store for 16 more gallons of LC (10%).
• Add 4 gal (21) of LC (8.25%), test after 30 mins FC = 26 (yikes). Conducted 2 additional test from different locations with similar results.
• Started to brush for the first time and tested after 30 mins. FC = 9.6
• Add 4 gal (25) of LC (8.25%), continued to brush and tested after 30 mins. FC = 12.5
• Add 3 gal (28) of LC (10%), brushed then tested after 30 min, FC = 16.5
• Add 2 gal (30) of LC (10%), brushed then tested after 30 mins, FC = 19.0
• Tested 30 mins late, FC = 18.5
• Tested 60 mins later, FC = 18.0
• Tested 60 mins later, FC = 17.0
• Added 1 gal (31) of LC (10%), tested 30 mins later 18.5
• Tested 120 mins later, FC = 15.
• Ran out of FAS-DPD (0871) and no store are open.
• Added 2 gal (33) of LC 10% to carry me through the night. Only means of testing FC are test strips which indicate FC above 10.

As of today, pool has turned from green to grey and continue to show improvement. Recent readings are:

• CYA-30
• PH-7.2
• FC-Still above 10 (using test strips)
• TA-90

Any thoughts on what I did right or wrong? Any concern of side-effects...other than damaging the liner? I'm hoping that I had a bad case of algae that I may finally rid this pool of!

 

[mknauss]

Welcome to the forum!

First thing I notice is you were above the SLAM level of FC based on your CYA quite often. That excess chlorine is very susceptible to UV burn off.

I doubt there is much chance of any liner damage. That is typically found when using granular solid chlorine, not liquid.

You will find it difficult to find reagent in stores for the FAS-DPD test. I suggest ordering from TFTestkits.net.

You are now in the Pool Owner Patience pattern. Sand filters take the longest to clear a pool when SLAM'ing.

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Take care

 

[jblizzle]

We might have had a better idea if you posted the CC test results with each FC test result.

But absent of that, the slam process will just take the amount of chlorine that it takes. There is no estimating the amount of chlorine required.

By the way you can save yourself a lot of reagent by using 10 mL of water for the fas-dpd chlorine test so that each drop is 0.5 PPM.

Oh, looking closer it appears you were going significantly above the shock level required for your cya, so that will result in higher losses to the Sun.

 

[rotortool]

You are correct and I am SLAM level FC is higher than my CYA of 30 recommends so burnoff should be expected. I have the reagent replacement on order already since I expect it to be difficult to find.

I was hoping to hear that patience is what I need now!

Thanks

 

[rotortool]

Didn't think about doing the CC test and will do that next time. Still learning.

Anticipating I would run out, I did switch to the 10 mL method towards the end. Great point.

My CYA is 30 and Temperature was only 55 and cloudy. Recommended shock level is 12 and I was targeting 15, I appreciate the comments and will scale back in future efforts.

 

[jblizzle]

Given that you had a CYA reading and the FC was not completely disappearing very quickly it's actually likely that your CCs would have been near zero the entire time anyways. So no worries not testing it.