Black / Dark Brown Pool Sand. Is this normal?

Prospero423

Member
Jul 28, 2013
6
West Monroe,La
I opened my sand filter to perform a deep clean in preparation for opening the pool for the season and I noticed that my filter sand is a very dark brown / black color. It doesn't look like the sand in the TFP deep cleaning video. I replaced the filter sand when I bought our house about 6 years ago and the old sand did look similar. I thought it was a different type of filter medium that the original owners used and I just replaced it with new pool filter sand. It doesn't look anything like pool sand I put in. During the day my pool normally looks pretty crystal clear. At night with the pool lights on, it does have a slight cloudiness to it with fine particles floating around.

So my question, is this normal for pool sand? If not, is there anyway to clean/refresh the filter without having to replace the sand?

My pool is approx 30,000 gallons with well water and swg.

Thanks.
 

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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,866
Tucson, AZ
Take some of that sand and soak it in a cup with vitamin C tablets crushed up and mix it around really well. Does to color of the sand change at all?
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,866
Tucson, AZ
Your sand is basically coated with iron oxide (rust) which is coming from your well water. The chlorine in your pool oxidizes the soluble ferrous iron (Fe2+) to insoluble ferric iron (Fe3+). The fine iron precipitate gets trapped in the filter and coats the sand.

Cleaning the sand could be tricky. Removing all that iron could take a lot of ascorbic acid and it may just be cheaper to toss the sand and start with fresh. However, the problem will return as the source of the iron is the fill water from the well. You might consider pretreating the water you put in the pool if it’s cost effective.
 

Prospero423

Member
Jul 28, 2013
6
West Monroe,La
Your sand is basically coated with iron oxide (rust) which is coming from your well water. The chlorine in your pool oxidizes the soluble ferrous iron (Fe2+) to insoluble ferric iron (Fe3+). The fine iron precipitate gets trapped in the filter and coats the sand.

Cleaning the sand could be tricky. Removing all that iron could take a lot of ascorbic acid and it may just be cheaper to toss the sand and start with fresh. However, the problem will return as the source of the iron is the fill water from the well. You might consider pretreating the water you put in the pool if it’s cost effective.
OK. Thank you for your help.
 

splashpad

Bronze Supporter
Aug 2, 2017
1,994
SE Kansas!
However, the problem will return as the source of the iron is the fill water from the well. You might consider pretreating the water you put in the pool if it’s cost effective.
So I've been wondering, is there a reason those hose/inline iron removing filters can't be setup on the existing pool water?
Is it because the water can't be isolated?
Apologies for going slightly off topic.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,866
Tucson, AZ
So I've been wondering, is there a reason those hose/inline iron removing filters can't be setup on the existing pool water?
Is it because the water can't be isolated?
Apologies for going slightly off topic.
They’re typically junk and don’t work very well or have very limited holding capacity AND chlorinated water rapidly destroys most ion exchange media. So they could be used as a hose-end filter for topping off (although it will be difficult to determine if they’re actually working) but they cannot be setup in the pool plumbing.
 
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splashpad

Bronze Supporter
Aug 2, 2017
1,994
SE Kansas!
They’re typically junk and don’t work very well or have very limited holding capacity AND chlorinated water rapidly destroys most ion exchange media. So they could be used as a hose-end filter for topping off (although it will be difficult to determine if they’re actually working) but they cannot be setup in the pool plumbing.
I meant as a temporary setup w/sump, not permanently installed 😄
I wondered about the chlorine
 

Prospero423

Member
Jul 28, 2013
6
West Monroe,La
I meant as a temporary setup w/sump, not permanently installed 😄
I wondered about the chlorine
I purchased a CuLator FillFast last summer but I don't know how well it worked. We had a lot of rain last year so I didn't need to add a lot of fill water to my pool.

Cleaning the sand could be tricky. Removing all that iron could take a lot of ascorbic acid and it may just be cheaper to toss the sand and start with fresh. However, the problem will return as the source of the iron is the fill water from the well. You might consider pretreating the water you put in the pool if it’s cost effective.
I have a large bucket of ascorbic acid. So I might try to just circulate water between the pump and filter with the acid to see if I can't get the sand cleaned. I can always replace the sand, but like you said, I'm always going to have this problem so I'll need to play around with different options to see if I can get anything to help.
 
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splashpad

Bronze Supporter
Aug 2, 2017
1,994
SE Kansas!
I purchased a CuLator FillFast last summer but I don't know how well it worked. We had a lot of rain last year so I didn't need to add a lot of fill water to my pool.
See that's my thought :) Hook it to a sump w/garden hose & filter the existing water (especially since you already have it). I wonder if a Metal sequester or sequestering agent would help or hurt with one of those?

I have a large bucket of ascorbic acid. So I might try to just circulate water between the pump and filter with the acid to see if I can't get the sand cleaned. I can always replace the sand, but like you said, I'm always going to have this problem, so I'll need to play around with different options to see if I can get anything to help.
Agreed,
I wonder if you could somehow feed the return water through those filters, as the ascorbic acid breaks it loose, mostly capturing it? (instead of redistrubting it)
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,866
Tucson, AZ
I purchased a CuLator FillFast last summer but I don't know how well it worked. We had a lot of rain last year so I didn't need to add a lot of fill water to my pool.



I have a large bucket of ascorbic acid. So I might try to just circulate water between the pump and filter with the acid to see if I can't get the sand cleaned. I can always replace the sand, but like you said, I'm always going to have this problem so I'll need to play around with different options to see if I can get anything to help.
I’d just dump a bunch of ascorbic acid into the filter tank and let it sit. Maybe mix it up with a broom handle (don’t break the laterals!). Then drain it. You want to be really careful not to get AA into the pool or else it’ll neutralize your chlorine and you’ll be fighting a battle against it until it’s all gone.
 
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