I Opened My Pool and Stains Are Gone

mmcwhorter

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Jul 13, 2015
212
Huntingtown, MD
With that title, I am not complaining...but want to post this for comment: So, for the last two years I have noticed a "charcoal grey...dark stain" in the deep end, on only one side of the drain, on the order of 3 feet by 2 feet, sort of a kidney bean shape. If I search, I can probably find a photo taken after SLAM on a calm day....with still water. Clearly evident. Would not brush off, was not dirt or organic in nature. Assumed but cannot prove it was Iron, but prior to opening this season, I had bought some VIT C tabs was planning to use them on the "Iron Stain" in a weighted sock this week. So, I opened my pool within the last 7 days and after SLAM and all the grubby organic matter has lifted off the bottom, I am happy to report I noticed the stain is gone. No complaints, but I also assumed naturally the iron had gone into solution with the water...Since I needed to test for Salt content at the Pool store (and get needed muriatic acid)....and their standard water tests for Iron and Copper.... To my surprise....both were 0 ppm. Not 0.0001 ppm, but 0.000. Now, last year when I closed the pool (October) I know for sure I have non-zero Iron and Copper. I just assumed the number for Iron when I opened would be a bit higher due to the stain being gone. But, no!!! It's Zero. So, I am at a bit of a loss to account for BOTH the (assumed) Iron stain having vanished over the winter and B) having the pool store reading at completely nothing for the Fe/Cu Metal content...Ideas? Now, what to do with the VIT C? I guess I can consume it... LOL>
 

Texas Splash

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I suppose it's possible that over the winter your FC level dropped enough to where the iron (assumed) could go back into solution. As for the pool store testing ... well ..... we sometimes go there for metals testing, but just like many of their tests, it's hit & miss. I guess you'll find out soon enough when you increase the FC and watch for stains to reappear. If they do, you can have that Vitamin C ready to test.
 

mmcwhorter

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Jul 13, 2015
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Huntingtown, MD
Well, FC was at 0 when I took the cover off...as expected. As I was cleaning the debris out of the pool...and slowly adding CYA (from near 0 to about 40) over a period of 4 days...I twice added 73% Cal Hypo. One pound at sunset on two successive days, i dissolve it almost completely in a 5 gal bucket of pool water and equally distribute it around the pool...CYA might have only been at 20 by then.........took the FC up to about 4 PPM both days by dark. The next morning, on both days, FC=0 and CC= 3...makes sense to me. A mini Pre-SLAM??? I have since SLAM'ed for real last night, took it up to FC=12...and this morning I was at FC=11, CC= 0.5......water is crystal clear. So I think I'll keep FC above 7 till sundown today...add a little more Cal-Hypo before bedtime, and expect to be good to go and complete SLAM tomorrow. When FC gets down to about 5, I'll fire up my Pentair SWG....water temp just hit 70F....I'll keep an eye out for that stain to re-appear. Didn't think about that.
 

mmcwhorter

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Jul 13, 2015
212
Huntingtown, MD
And also, I had fairly high phosphates at the close last year....something like 250 ppm...And that too also measured "0" at the pool store this week. I assume that got consumed by algae over the winter/early spring? I love it when they try to sell me expensive phosphate removers and I tell them about the SLAM process....LOL>
 

mgtfp

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I'm wondering if you had ammonia in your pool, i.e. bacteria turning CYA into ammonia. That usually also results in low pH which would have helped with the iron stains.

What did your pH do through all of this?
 

mmcwhorter

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Jul 13, 2015
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Huntingtown, MD
Oops, My phosphate reading was a typo...It was 250 ppm last summer in the middle of the open season, and that's when the pool store folks pushed me to the Phosphate Treatment. My pool was perfectly clear and I told them to look at this website for accurate information.... There may be Algae Food in the pool, but after a SLAM there is no algae to eat it. Reminds me of a closed McDonalds eatery at 3 AM...there may be bad stuff there, but no one there to eat it. :)
 

mmcwhorter

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Jul 13, 2015
212
Huntingtown, MD
As to the Stain....it's back after SLAM. I guess it'll be using those VIT C tabs after all.

Pool water looks fantastic, you can read the date on a dime coin at the deep end... LOL....although we are suffering thru a very cold spring (44F this morning, and we are not going to rise above 70F at any time for the next week). I SLAMmed with a little higher than the required amount of CL this year using 73CALHYPO....was around FC=14-16 during SLAM with CYA was 40 when I passed SLAM requirements. I passed SLAM on the second morning, nice. I waited about 5 days for the FC to drop, I guess because it's been so cold and cloudy here....and today fired up my SWG to 60% when it got below FC=7...

Today's measumrements with brand new TF-100 test kit refills:
FC= 6.5
CC= 0
CYA= 90 (I think may I added just a little too much Stabilizer as I was targeting 70-80)
TA= 100
CH: 350 (CH was 250 before SLAM, seems like a lot higher than it should today after adding about 8 pounds 73CALHYPO total during SLAM since pre-SLAM 250 reading)
TA=100
pH=7.4

As to the 250 vs. 350 CH reading, 250 was measured with one-year-old reagents, 350 with brand new out of the box...Maybe that is the difference. I expected to see it rise about 25 ppm per POOL MATH...

Happy Pool, my Dolphin is working great....the early Spring leaves have stopped falling, a little cold, working on the Stain next. I sure do miss Global Warming :p
 

mmcwhorter

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Jul 13, 2015
212
Huntingtown, MD
My pH has been very stable throughout the entire SLAM and up to today. I took it down to around 7.2 about a week ago for the SLAM using MA. Probably a little too low...but alls well that ends well. After a week, it's maybe 7.4. This is uncommon for my pool, which historically has been a very bouncy pH...very acid hungry. Last 5 years it would not be uncommon to take it down to 7.4 and find it at 8.0+ a few days later. I think keeping the TA higher (in the 90 range) might help buffer this bounce.
 

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ajw22

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Higher TA helps your pH rise more rapidly.

Run your TA at around 60 to minimize pH rise.

What is the pH and TA of your fill water?
 

mmcwhorter

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Jul 13, 2015
212
Huntingtown, MD
I was under the impression high TA helps to keep the pH from bouncing, i.e. rising quickly. Hmm, gonna need to re-think this maybe? Have not really used any fill water at all. When the pool cover came off, the water was actually a bit high...which was useful for Vac to Waste getting the crud out of the bottom. And we have had a couple of inches of rain since. So, no fill water from the hose has been used. It's a deep well, 230 feet. Good idea for me to measure and record it when I have the time.
 

IceShadow

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I was under the impression high TA helps to keep the pH from bouncing, i.e. rising quickly. Hmm, gonna need to re-think this maybe? Have not really used any fill water at all. When the pool cover came off, the water was actually a bit high...which was useful for Vac to Waste getting the crud out of the bottom. And we have had a couple of inches of rain since. So, no fill water from the hose has been used. It's a deep well, 230 feet. Good idea for me to measure and record it when I have the time.
TA is there to prevent your pH from crashing unexpectedly. High TA will cause a steady rise due to offgassing CO2 (accelerated by any aeration that happens, like people playing in the pool or water features). Different pools have a different level of TA that keeps their pH relatively stable. Mine is around 80 or so, and is doing well there - but I don't have water features or a lot of aeration happening currently (not a lot of pool use here, still a bit chilly most days).

People who use pucks for chlorination need that TA at a higher level, since pucks are highly acidic. Liquid chlorine is pH neutral in the final action of it, so doesn't require as high of a TA to keep things stable.
 
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