Unknown Stain on Pebblecrete Floor

[silver_pear]

Hi all. I've been battling what I assumed was an algae breakout in my pebblecrete pool. I noticed it properly Thursday night, but in honesty I feel like I have probably noticed it for longer.

Effectively I assumed it was some form of algae outbreak as we've just come into summer in Australia, so I shocked the pool (even going up to the mustard algae shock level suggest in other threads). I brushed with both an algae brush and the normal nylon. I've repeatedly vacuumed the pool.

Nothing seems to be working! From what I can discern, the fact shocking the pool is having no effect indicates it likely isn't organic (i.e. not algae) and therefore likely metal? What's odd is the streaks going through it.

I try not to add much to the pool, but a few weeks ago I added some clarifier (Polyammonium Chloride). I'm not sure if it is related but figured it was worth mentioning.

Here are my test results/logs from Thursday (when I noticed the issue) to now (Tuesday). I raised the FC level well up over this time to shock the system. The pump has been running but SWG turned off during this time.

I've also attached pictures to try and demonstrate the issue. The photos where the pool looks bright are from Saturday around 2pm, while the dark photos are from Thursday prior to any treatment (around 6pm).

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Build Type: Plaster
Volume: 22500 liters
Chemistry: SWG
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Latest Test Result Summary:
FC: 17.5 (4 hours ago)
CC: 0.0 (1 day ago)
pH: 7.5 (1 day ago)
TA: 85 (2 days ago)
CH: 350 (2 days ago)
CYA: 51 (1 day ago)
SALT: 4700 (8 days ago)
CSI: -0.37 (4 hours ago)
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Test Results 2024-10-29 @ 07:36 am
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Free Chlorine: 17.5
CSI: -0.37

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Test Results 2024-10-28 @ 12:57 pm
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Free Chlorine: 21.5
CSI: -0.37

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Chemical Addition 2024-10-28 @ 09:07 am
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+ 0.5 Litres of Bleach

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Test Results 2024-10-28 @ 05:50 am
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Free Chlorine: 22.0
CSI: -0.37

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Test Results 2024-10-27 @ 08:50 pm
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Free Chlorine: 25.5
CSI: -0.37

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Maintenance 2024-10-27 @ 06:02 pm
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Cleaned Filter

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Chemical Addition 2024-10-27 @ 05:25 pm
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+ 500 Grams of CalHypo70

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Test Results 2024-10-27 @ 05:03 pm
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Free Chlorine: 15.0
Combined Chlorine: 0.0
pH: 7.5
CSI: -0.37

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Test Results 2024-10-27 @ 05:03 pm
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CYA: 51
CSI: -0.27

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Test Results 2024-10-27 @ 07:50 am
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Free Chlorine: 20.0
CSI: -0.26

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Test Results 2024-10-26 @ 09:54 pm
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Free Chlorine: 21.0
CSI: -0.26

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Test Results 2024-10-26 @ 01:16 pm
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Free Chlorine: 22.5
Combined Chlorine: 0.0
pH: 7.6
Total Alkalinity: 85
Calcium Hardness: 350
CYA: 48
CSI: -0.26

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Test Results 2024-10-26 @ 09:15 am
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Free Chlorine: 31.5
CSI: -0.60

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Chemical Addition 2024-10-26 @ 09:08 am
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+ 2 Liters of Bleach

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Test Results 2024-10-26 @ 07:42 am
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Free Chlorine: 22.5
CSI: -0.60

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Chemical Addition 2024-10-25 @ 06:37 pm
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+ 1 Liters of Bleach

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Test Results 2024-10-25 @ 05:39 pm
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Free Chlorine: 29.5
CSI: -0.60

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Chemical Addition 2024-10-25 @ 02:50 pm
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+ 500 Grams of CalHypo70

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Test Results 2024-10-25 @ 02:37 pm
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Free Chlorine: 21.0
CSI: -0.60

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Chemical Addition 2024-10-25 @ 01:20 pm
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+ 3 Liters of Bleach

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Test Results 2024-10-25 @ 12:56 pm
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Free Chlorine: 15.5
CSI: -0.60

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Test Results 2024-10-25 @ 08:44 am
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Free Chlorine: 19.5
CSI: -0.60

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Chemical Addition 2024-10-24 @ 10:12 pm
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+ 2 Liters of Bleach

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Test Results 2024-10-24 @ 10:04 pm
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Free Chlorine: 18.0
CSI: -0.60

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Chemical Addition 2024-10-24 @ 07:37 pm
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+ 4.5 Liters of Bleach

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Test Results 2024-10-24 @ 06:15 pm
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Free Chlorine: 7.0
Combined Chlorine: 0.0
pH: 7.5
CSI: -0.60

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Test Results 2024-10-24 @ 06:06 pm
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CYA: 75
CSI: -0.51

 

[ajw22]

Welcome to TFP.

First thing I would do is confirm your pool passes a Overnight Chlorine Loss Test

Assuming it does, then put some crushed up vitamin C in a sock and rub it on the stains and see if they lift. If they do it is iron staining.

Metals - Further Reading

www.troublefreepool.com

Copper in Pool Water - Further Reading

www.troublefreepool.com

Stains in Your Pool

The stained pool is beyond embarrassing. Our in-depth Guide to remove stains in your pool will help you to remove the stains and prevent them in the future.

www.troublefreepool.com