Yellowish Staining/Scaling (or Algae?) on Above Ground Pool

[roamin]

Sorry to make this opening so long, but want to try and cover how I got here as best I can (TL/DR below)...

A couple months ago when I first started working on the pool after winter, I upped the CYA level to 40 from 0, and added chlorine to mustard algae shock levels and maintained that for about 4 days (water only had a slight green tinge, no presence of mustard algae was detected, but we had a problem with it at the start of last year so just wanted to be safe). Water was crystal clear after two days, just still too cold to swim.

Since then, we've had TONS of rain and I knew the CYA would be getting lower, and instead of testing FC regularly like I should have, I've just been adding enough chlorine to ensure the FC stayed above 10 (too high, I know, especially if CYA has gotten lower). I know I should've been testing every day, but it was easier just to tell my son to go add X amount of chlorine and err on the side of too much to make sure no algae started growing before I had time to work on opening the pool. (this was the similar to the method I used over the winter, which I know caused FC levels to get too high at times because it bleached the blue diamond pattern out of the liner)

About 3 weeks ago we went out of town for several days and neighbor forgot to add chlorine for me, and when I got back the FC was at 0 and water was clear but had a slight green tinge again (barely this time), so I upped it to shock levels again and continued with my "make sure you have enough" method described above. Water was clear/colorless and sparkling again after just a day.

In the weeks since, it's developed a yellowish stain covering most of the liner AND the ladder with random spots that aren't stained. The sides don't feel slimy or rough at all, and no matter how hard I brush, it won't come out/off. When I tested the FC yesterday, it was at 15 after not adding chlorine for two days, so I know the FC level has gotten WAY too high. Not sure whether I'm dealing with a true stain, or some sort of scaling (with maybe dirt or algae mixed in?). The pool sits under a large oak so when it rains we got lots of yellow pollen and leaves in the pool regularly during the spring, which tends to turn the water yellow for a day when it happens.

TL/DR: I have a yellowish stain or scaling of some sort on pool liner AND ladder. I don't think it's algae because FC levels have been consistently high (even way too high) for 3 weeks and water is clear, but realize it could be. Walls are not either slimy or rough feeling. I've only (ever) used liquid chlorine and dry stabilizer on the pool (MA one time last year).

Test yesterday evening:
FC: 15

Test this morning:
FC: 14
CC: 0
pH: 6.8 (may be lower, as that's the bottom of the range on the test)
TA: 140
CH: 75
CYA: 20

Any help or guidance someone may have is greatly appreciated! Thanks!

 

[Texas Splash]

Iron? You on a well? Try rubbing some Vitamin C tablets on the stained areas.

 

[splashpad]

... the blue diamond pattern out of the liner) ...

pH: 6.8 (may be lower, as that's the bottom of the range on the test)

Vinyl Pool, get the PH and CYA up

 

[roamin]

Iron? You on a well? Try rubbing some Vitamin C tablets on the stained areas.

No, city water supply, plus I haven't added water from the tap at all this year. Only additions have been rain water (that's "filtered" through the branches of the huge oak tree the pool sits under).

Heading to buy some Vitamin C tablets at lunch to try this (I'm assuming I can get these a drug store like CVS or Walgreens?)

 

[Texas Splash]

Yes, Walgreens, CVS, or Walmart should have regular tablets. Due to the shimmer of that clear/tinted water, it would be a good idea to check.

 

[roamin]

Vinyl Pool, get the PH and CYA up

Yeah, I was shocked the pH was so low. For two years it's pretty well stayed solid between 7.4 and 7.8. It tends to go down a bit when the solar cover is on, and I'd just aerate for a bit to bring it back up, so I'd gotten used to not paying too much attention to it. The cover has been on all winter, so maybe it's dropped so much because of the extremely high chlorine levels and the cover being on (my uneducated guess, anyway). I opened up the aeration valve on the water return side this morning to start bringing it back up. Still need to add CYA.

 

[roamin]

Iron? You on a well? Try rubbing some Vitamin C tablets on the stained areas.

Here's a pic after the Vitamin C tablet test... was like an eraser on a dry erase board, wiped it right off with barely any pressure. To make sure it was the tablet doing the work, I rubbed another section fairly hard with just my finger, and it didn't do anything.

I did think of three potential sources for metal to leach into the water:

1. I have a portable propane water heater that I use on the pool at times (to extend the swimming season a bit) that has copper heating coils. Haven't used it yet this year, but used it a lot in the fall last year.
2. The pump for the heater has two garden hoses running into the pool, no idea what kind of crappy metal the end connectors are made out of
3. The garden hose on the inlet side of the heater's pump has a stainless steel mesh filter screwed onto it to stop large particles from circulating through the pump and filter.

Is this maybe just a case of pH getting too low and leaching metals out of one or all of those parts and into the water? Regardless of how it got there, I guess... tips on what to do next to get rid of it? I mean, it's a fairly small pool... I could hand my kids a couple bottles of Vitamin C tablets and set them to work , but I'm thinking that would just get it off the wall, and not out of the water.

 

[Texas Splash]

Is this maybe just a case of pH getting too low and leaching metals out of one or all of those parts and into the water?

That is a possibility. A low pH can and will damage equipment. However when I think of heaters I think of copper elements, not iron. Vitamin C shouldn't have such a dramatic effect (if any) on copper. I do believe you should look at those areas you pointed out, however the Vitamin C points to iron. Iron usually reacts more when the pH is elevated, but yours is low. I can only imagine what the water would do if the pH was actually within range.

Regardless, in a pool your size it's more economical to just change the water rather than to try and control the metals, that is IF the replacement water is metals-free. But you do have a couple choices for the staining. You can just fill some thin socks or nylons with Vitamin C and hand treat the stains, or order some Ascorbic Acid (AA) and do an AA treatment. Once the staining lifts, then dump the water and start over.

Ascorbic Acid Treatment - Further Reading

www.troublefreepool.com

 

[roamin]

That is a possibility. A low pH can and will damage equipment. However when I think of heaters I think of copper elements, not iron. Vitamin C shouldn't have such a dramatic effect (if any) on copper. I do believe you should look at those areas you pointed out, however the Vitamin C points to iron. Iron usually reacts more when the pH is elevated, but yours is low. I can only imagine what the water would do if the pH was actually within range.

Regardless, in a pool your size it's more economical to just change the water rather than to try and control the metals, that is IF the replacement water is metals-free. But you do have a couple choices for the staining. You can just fill some thin socks or nylons with Vitamin C and hand treat the stains, or order some Ascorbic Acid (AA) and do an AA treatment. Once the staining lifts, then dump the water and start over.

Ascorbic Acid Treatment - Further Reading

www.troublefreepool.com

Water change...ugh. Easy enough, I guess, but still a pain. I'm assuming I can do it in stages? I know it'll take longer and I won't get necessarily get all of it, but, I don't want to completely drain the pool and risk dealing with the legs moving again when I re-fill it (long story, documented in my pool build post so I won't go into it here).

Now the real question... is it safe to swim once I get the FC and pH levels corrected? That's the only question my kids and wife will care about.

 

[Texas Splash]

Now the real question... is it safe to swim once I get the FC and pH levels corrected?

Sure. The iron staining and discoloration is just a nuisance.

 

[Texas Splash]

You might also consider making a way to run water though a bucket with polyfill in it. Or just polyfill in the skimmer if you have one. It can make a big difference. The more you remove now the less water you have to exchange.

 

[roamin]

You might also consider making a way to run water though a bucket with polyfill in it. Or just polyfill in the skimmer if you have one. It can make a big difference. The more you remove now the less water you have to exchange.

Cool idea. I still have the original (crappy) canister filter that came with the pool, so I should be able to set something like this up pretty easily without having to mess with my existing pump/circulation.

To make sure, you're talking about the kind of polyfill material pictured below, right?

 

[Texas Splash]

That's it!

 

[roamin]

That's it!

Awesome! Thank you so much for your help!!

 

[roamin]

For anyone who happens upon this post in the future... from the Ascorbic Acid Treatment article that @Texas Splash linked to above...

When there is iron in the water, low PH (say around 7.0 to 7.3) tends to prevent staining while high PH (say around 7.8 to 8.2) tends to cause staining. Phosphonic acid helps control this, so that high PH levels can occur without staining. High FC levels also tend to cause staining. As the PH goes up, and/or the FC level goes up, the chances of staining increase. Likewise, as the phosphonic acid level goes down, the chance of staining increases.

So it does appear that my ridiculously high FC level (and stupid, "make sure you have enough" method of maintaining said level) may have lead to my issue here despite the low pH. Lesson: Doing things the right way in the first place is always easier in the long run.