Trouble With FC Test TF-Pro Kit

[mhk5042]

Hello I’m a new pool owner and purchased the Tf-Pro kit. I’m having trouble with testing and SLAMing my pool.

I’m at a loss and feeling defeated. No matter how much calcium hypochlorite I add the FC doesn’t not go higher than 7.5. The real kicker is that the most recent test about 2 hours after adding 3 lbs of cal hypo the FC level was at 2.5.

I’m not sure what is wrong or what I’m doing wrong. Am I conducting the fas-dpd incorrectly? I followed the directions and mark how many drops it took for the mixture to turn clear. However the vial does eventually turn back to pink after being clear for 15 seconds but I am not continuing the test.

Below is my recent history.


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Test Results 05-12-2025 @ 08:31 PM

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Free Chlorine: 2.5

CSI: -0.25



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Test Results 05-12-2025 @ 07:48 PM

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Free Chlorine: 7.5

Combined Chlorine: 3.5

CSI: -0.25



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Chemical Addition 05-12-2025 @ 06:53 PM

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+ 3 Pounds of CalHypo70



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Test Results 05-12-2025 @ 06:14 PM

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Free Chlorine: 6.5

Combined Chlorine: 2.5

CSI: -0.25



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Chemical Addition 05-12-2025 @ 05:14 PM

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+ 3 Pounds of CalHypo70



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Test Results 05-12-2025 @ 04:48 PM

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Free Chlorine: 5.0

CSI: -0.25



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Chemical Addition 05-12-2025 @ 03:20 PM

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+ 3 Pounds of CalHypo70



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Test Results 05-12-2025 @ 02:52 PM

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pH: 7.4

CSI: -0.25



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Chemical Addition 05-12-2025 @ 01:55 PM

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+ 0.34 Gallons of Baume31



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Test Results 05-12-2025 @ 01:54 PM

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Free Chlorine: 1.2

Combined Chlorine: 3.2

pH: 7.7

Total Alkalinity: 143

Calcium Hardness: 197

CYA: 21

Temperature: 67°F

CSI: 0.05



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Test Results 05-12-2025 @ 12:09 PM

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Free Chlorine: 2.5

Combined Chlorine: 2.0

pH: 7.6

Total Alkalinity: 170

Calcium Hardness: 325

CYA: 20

Temperature: 64°F

CSI: 0.20



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Chemical Addition 05-11-2025 @ 11:02 PM

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+ 2 Pounds of CalHypo65



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Test Results 05-11-2025 @ 08:47 PM

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Free Chlorine: 2.5

Combined Chlorine: 1.5

pH: 7.6

Total Alkalinity: 170

Calcium Hardness: 300

CYA: 20



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Chemical Addition 05-11-2025 @ 07:46 PM

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+ 35.75962160078512 FluidOunces of Baume31



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Test Results 05-11-2025 @ 02:43 PM

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Free Chlorine: 2.5

Combined Chlorine: 2.0

pH: 8.0

Total Alkalinity: 180

Calcium Hardness: 300

CYA: 20



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Test Results 05-09-2025 @ 08:24 PM

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Free Chlorine: 2.0

Combined Chlorine: 4.5

pH: 7.8

Total Alkalinity: 180

Calcium Hardness: 300

CYA: 20

 

[mhk5042]

I’ll also add that I have a 20K gal, IG plaster pool with a DE filter near Philadelphia, PA.

 

[Rancho Cost-a-Lotta]

Trying to use calcium hypochlorite for a slam is next to impossible. It dissolves too slowly. Switch to liquid chlorine and continue on.
SLAM Process

 

[PoolStored]

Go here:
Ocean State Job Lot
808 E Street Rd, Warminster, PA 18974

And get liquid chlorine instead of cal-hypo. Best price around.

However the vial does eventually turn back to pink after being clear for 15 seconds but I am not continuing the test.

Correct. When it turns clear, you are done.

 

[JamesW]

The CC numbers indicate a problem like ammonia.

What was your previous CYA reading?

 

[mhk5042]

Last year was the first year at this house and the prior owners recommended a local pool company. It looks like the stabilizer level (does not say CYA) was listed at 170. When I opened the pool the CYA was at 20.

The CC numbers indicate a problem like ammonia.

What was your previous CYA reading?

 

[sande005]

Having just spent the winter in that area, and having been previously, there are a lot of dissolved minerals in the water. Adding Cal Hypo will drive up your CH, and take the CSI out of range. Only use liquid CL, as noted above. You'll save a lot of money, too.

Your CC is very high - there are a lot of organics combining with the active chlorine. So it is getting used quickly.
As @JamesW just suggested, there may be an ammonia issue. Test your CYA again, and report back. That and a test for how fast added CL gets used up, will tell the tale about ammonia.
Ammonia - Further Reading

Consult with us about how the testing for ammonia went, before going on to the following!

How's the water look? Crystal clear, cloudy, murky, or a swamp? Post pictures, so we can advise.

Your earlier CYA's (one looks to be a pool store test) are low, but not terrible. So sunlight can also be burning off some additional active CL before it gets much of a chance to do anything.

The Overnight Chlorine Loss Test (OCLT) can definitively diagnose whether you have an algae problem or not. Perform the Overnight FC Loss Test (OCLT)

Before you start adding CYA though, read through the SLAM process. SLAM - Shock Level and Maintain
Read it again. And then one more time. Print it out, and start to follow it to the letter. With lower CYA, you'll need less CL added to reach the SLAM level, although you will have to monitor it more frequently. It may take days, or even a couple of weeks if really bad, depending on the current condition of the pool.

If you download and use the PoolMath app, and pay the high cost of $$8/yr (gasp!) to subscribe, you can log there all your tests and additions. Use the same user name there as here, and we can see your history - no more typing long posts. Click on my user name in this post to see my logs and my lurching toward full startup.

 

[JamesW]

Last year was the first year at this house and the prior owners recommended a local pool company. It looks like the stabilizer level (does not say CYA) was listed at 170. When I opened the pool the CYA was at 20.

The loss of CYA points to a possible ammonia issue.

This can take a LOT of chlorine to oxidize completely.

Keep at it and it will eventually break.

If it is ammonia, you should see a steady drop in pH and TA.

What does the water look like?

 

[JamesW]

Ammonia - Further Reading

www.troublefreepool.com

 

[mhk5042]

The loss of CYA points to a possible ammonia issue.

This can take a LOT of chlorine to oxidize completely.

Keep at it and it will eventually break.

If it is ammonia, you should see a steady drop in pH and TA.

What does the water look like?

Thank you for your quick reply’s! The pool is mostly clear. This is a picture of it yesterday before I added cal hypo today. When the pool was open it was still clear but with some leaves in the pool. It took about 6 full cycles of my s200 dolphin to clear out the debris.

I’m working on linking my google account with my TFP account but here is a link to the pool: PoolMath Logs

 

[JamesW]

Continue SLAM to completion.

 

[sande005]

13 lbs of Cal-Hypo last night??? Hope that is a mistype.

@JamesW is the pro - so if he says to do the SLAM, do it and not worry about ammonia.

Off to Ocean State for you today, to buy several cases of Liquid CL.
808 E Street Rd, Warminster, PA 18974

Your CH should have increased by about 40 in about the last day due to the Cal-Hypo (assuming the 13 was really 3). Still fine now, but need to stop it or by the end of the SLAM you could be in a bad spot. Then the only option is to partially drain the pool. As noted, the slower dissolve/incorporation will always keep you behind the curve in hitting your SLAM targets.

Retest your CYA, but bring the sample inside and let it warm up first. It can be affected by cooler water. Your pool isn't all that cold, so it may not change, but good to verify.