Inorganic stains...ugh!

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C3Cl3N3O3

C3Cl3N3O3

0
Bronze Supporter
May 25, 2015
460
Fort Mill, SC
Pool Size
20000
Surface
Vinyl
Chlorine
Liquid Chlorine
OK I've been wrestling with this on and off for years. I have some staining issues on my liner. In previous years, it affected the white stairs really badly as well. This year the stairs don't looks too bad. The deep end really isn't affected that much except on the corners of the liner, but the shallow end is badly stained. My numbers are as follows:

pH: 7.6
TA: 70
CYA: 45
FC: 8

I'm doing straight BBB and haven't used algecides or any other pool store chemicals in two years. In the past, the pool store told me my copper was elevated. I have a Taylor kit, but no metal tests.

I did a quick 10 minute test of a puck and a sock filled with Vitamin C. The puck didn't clear it up, but it responds immediately to the Vitamin C. Here is a photo that shows the sock slid up off the test spot a bit.

Stains.JPG


So I assume this is inorganic (metals?) A year or two ago I came to the same conclusion and treated it with Natural Chemistry Stain Free/Metal Free combination. I followed the instructions to the T. It really didn't clear things up very much. I just went ahead and cleaned the stairs with the darn Vitamin C. So what's a better game plan here? For the moment I'm just moving that sock around.
 
I think you're absolutely correct on the copper. True, algaecides are a major contributor to copper. I don't see your equipment listed, but some heaters are factors as well if you have one. You mentioned replacing most of your water in the past, but unless it was a significant drain (or partial) and subsequently refilled, it may not have been as efficient as anticipated leaving enough copper behind to react with your chlorine (FC). Really hard to know. While you could use a sequestrant to help "bind" any remaining metal to prevent more staining, any existing staining would require more of an ascorbic acid treatment.

You might like to ready these threads: Ascorbic Treatment to rid Pool of metal stains and Stains on vinyl returned after clearing up.

Hope that helps.
 
OK so I have a bit more info. I don't have a heater. I hit the pool store up for a water test (always interested in cross-checking with my own results). :) My iron and copper are both zero. I do have 500 ppm phosphates, though. My research on TFP indicates that this is nothing to be concerned with. But that's the only metal that showed up. So there's no correlation between phosphates and metal stains then?

So these stains have more or less been around for a while. The pool store thinks that all the metal left the water and formed the stains. That just seems suspicious to me. I will say that when I opened the pool, the stains were less noticeable and my pH was 7.0 or so (although my memory might be suspect). Now my pH has drifted up to 7.6. I understand higher pH can correlate with metal stains, but to the point of a zero iron and copper water test reading?

I'll run the pH down to 7.0 and FC to zero and start the AA treatment followed by the sequestrant (one big dose and then maintenance doses), I guess. I'm confused.
 
One of the problems with testing pool water that it already has chlorine added to it and that it skews the test. The metal has already precipitated out of the water and onto the pool surface because of the chlorine, so the test is not as reliable - hence the "zero metals" result. Phosphates feed algae but have nothing to do with metals, so you can ignore that one. You're two biggest influences on water with metal in it is in-fact the pH and FC. When you know you have metal in the water, it's a balancing act. Ideally you hope to remove the metal water completely, or at least exchange enough of it over time to where the levels are so low you don't have to use a sequestrant anymore.
 
So it sounds like the sequester and filter out thing is a pipe dream, I'll need to keep it sequestered long enough to replace the water over time (and hopefully not add any metals back in!)

What about something like this though?

https://www.amazon.com/Assist-Enhancer-Caribbean-Blue-Chemicals/dp/B01EVWSZWC

After I sequester, juice my sand filter with that which temporarily gets it down to 5 microns. Run it for a few hours, then backwash to the waste line. Still a pipe dream?
 
Very unlikely that you can filter out the metal. You can do the same thing as the filter aid by adding DE, Pool School - Add DE to a Sand Filter. The best bet is lift the stain, sequester it and drain. I don't know what kind of pool you have so I can't advise on draining. You can add your pool info to your signature and we can better help you, Pool School - Read This Before You Post
 
That's right, very low risk and if it works great! If not, your water is a little cleaner. :)

If you do decide to drain to remove the metals be sure to leave a foot of water in the shallow end to prevent the liner from shifting or shrinking.
 

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OK gang here's my pool diary for the past two days. I improvised a bit from the TFP AA treatment in order to use the supplies I had on hand and get the pool closed and reopened quickly in time for a pool party.

So I had Natural Chemistry Stain Free, and it turns out it is citric acid and not ascorbic acid. I lowered the pH to 7.2 and FC to 1. I did a double maintenance dose of algecide. I added 2 lbs of Stain Free. It made a difference, however after 30 minutes the liner had major clean streaks going. I hit it with another half pound. Better, still a lot of isolated stains. I spot cleaned them with Vitamin C pills in a sock. It took a lot, probably another 1/4 pound. I didn't realize just how much the whole liner had darkened over time. After an hour or two of all this, it was very clean and much lighter. I hit it with the Metal Free mystery sequestrant (full bottle).

I didn't have any DE to juice the sand filter with. But, after running it overnight it increased by 2 psi. So maybe it filtered some of the metal out? It picked up something. The water remained crystal clear throughout this whole process. I didn't see much in the way of precipitants on the pool floor, looked like regular old debris to me, but I vacuumed it to waste for good measure this morning.

Also for good measure I dumped 8" of pool water and refilled using city fill water (approx 3000 gallons). So worst case that will permanently get rid of another 15% of the metals.

The pH looked to be lower than 7.0 last night. It didn't take much to get it back to 7.2, just enough soda ash to raise it .2. I'm running a fountain to keep it up as well. If it goes any higher I'll hit it with the dry acid.

The alkalinity crashed from 70 down to 50. I've got it back up to 65 with the soda ash and some additional baking soda.

I've raised the FC to 6. It looks to be losing about .5 ppm per hour. I'll keep an eye on it.

So I'll keep the pH at 7.2 for a few weeks. I plan to do maintenance doses of sequestrant and backwash aggressively to wage a war of attrition on these metals.
 
Well I've hit one snag. I had been bumping up my CYA to approx 45 prior to all this to deal with the full sun. So today after the treatment, I lost approx 6 ppm FC in 5 hours. I checked the CYA, and it is under 30. There's a bit of cloudiness to the test water, I'm guessing it is close to 20 ppm. Any ideas why that would be? The partial water change should have only cost me 5 ppm or so. This is not good. I'm doing an emergency increase of 10 ppm CYA tonight.
 
Most times I do a metal stain treatment, it seems like I have several days of high chlorine demand with slightly cloudy water. Just keep an eye on the FC and pH. Don't let either rise too much or you risk the metal stains coming right back. Keep the filter on 24/7 and the cloudiness will go away.

What you're describing sounds normal to me.

Sent from my SM-G900V using Tapatalk
 
Nice work! Sounds like some good progress. The CYA most likely dropped from all the backwashing and maybe some bacteria consuming it while the FC was low. +1 to keeping any eye on FC and getting it raised to minimum for your CYA, [FC/CYA][/FC/CYA], over a few hours at most.
 
The CYA thing is just odd. I only had the chlorine lowered for 24 hours.

The water is crystal clear. The cloudiness I referred to is the CYA reagent/water mixture. There's a slight bit of cloudiness, but I can still easily see the dot with the comparator tube filled to the tippy top.

So I guess one area where I am fuzzy is this one or two week period where I now have to keep the pH low and can't shock the pool. What process is occurring here that I am waiting on to complete? Is the citric acid breaking down and transferring the metals to the sequestrant?
 
This has been a strange year for CYA. There are many pools all over the US losing CYA. Much more than years past.

The 2 week low PH idea has been a matter of debate for a little while. If your PH tends to rise I might be inclined to let it rise 0.1 every couple of days and see what happens.

Right now, I am concerned about your FC. That does need to be raised slowly but quickly. :) Especially with your CYA issue. You don't want to add CYA until FC holds. You need to be adding bleach and trying to raise FC 1 or so ppm per hour until you get FC to hold at 2-3. Then add 30 ppm CYA and repeat raising FC to 4 and hold it there.
 
Because if bacteria is still in the pool consuming CYA you don't want to feed it. Adding chlorine will kill the bacteria first and once it holds the bacteria is killed and it is safe to add CYA and keep going.
 
I see. Well last night at dusk I raised FC to approx 5 ppm, and this morning at dawn it was still right at 5. It appears I'm past chlorine demand from AA or the mythical CYA eating bacteria and I'm just battling the sun right now.
 

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