Yellow stains in vinyl pool

[stev32k]

I have yellow staining in parts of the pool. At first I thought it was a mustard algae and added a copper based algaecide. However, when I tried to brush down the sides of the pool the yellow would not brush off. I checked the pH and found it to be less than 6.8 (6.8 is the lowest I read) so I added sodium carbonate then shocked the pool. The next day I collected a sample and took it to the pool store for testing. The results were:

Free chlorine 5.8
total chlorine 6.4
combined chlorine 0.6
pH 7.0
hardness 120
alkalinity 0
cyanuric acid 110
copper 1.02

The stain appears pale yellow and is somewhat spotty around the pool. It is most prominent on the sides directly opposite the water return nozzles at each end. The plastic return nozzles themselves have developed a very heavy yellow to almost orange color.

Some additional information: The trees around the pool are all live oaks which keep their leaves all winter and start shedding them about the middle of march. Prior to shedding leaves the trees drop acorns starting about the middle of January and continuing until about the first of march. There are a lot of very large trees and they produced a bumper crop this year. So when the acorns start falling and continuing until after the oak pollen has fallen about the first of May it's not unusual to get a bushel basket of acorns, leaves, and or pollen out of the pool every day. If the oak debris is allowed to set in the pool for extended periods (several weeks) the pH will get very low and the water will be stained with tannic acid.

In addition to the large oak trees we live close to a wetland (we used to call it a swamp) that has a lot of large pine trees and they shed pollen about the same time as the oaks drop their acorns. The pine pollen is a yellow color and it covers everything. The surface of the pool will be a bright yellow every morning and the filter backwash will have a definite yellow color during the season.

Short of some very expensive testing I don't know of any way to determine what caused the stain. It could be pollen, iron, organics from the oaks, some combination of these, or something entirely different. My question is what if anything can I do to remove the stains without ruining the liner? I've brushed the stained areas thoroughly with no effect. I would hate to drain the pool completely and then clean it off, but maybe that is the only answer. I would appreciate any suggestions. Thanks.

 

[duraleigh]

Hey,

Welcome to the forum.

Your description sounds like tannic acid stains. If that's true, run a slightly higher level of chlorine than normal (around 10-12ppm) for a few weeks and it will disappear. If it's not tannic acid, post back and we'll go from there.

I would suggest you use no more copper in your pool. You will get little encouragement for the use of copper on this forum. Chlorine will do the same thing....just better.

You need to shock your pool. The test result of .6ppm combined chloramines indicates that.

With that very high reading of 110ppm CYA, you will need to keep your FC much higher.....up around 8-10ppm at least and you will need around 30ppm to shock.

I know your only question was for the staining but the other items need attention so you can really focus on removing the stains.

Longer term, you should consider a partial drain and refill of your pool. First, to reduce the CYA somewhere manageable around 40-60ppm and Secondly, to reduce the level of copper in your pool.....there's no other way to get either of them out.

Pool School on the homepage (upper right corner) has a wealth of info on basic pool chemistry and normal levels. Read those articles and post more questions. Pool School is addictive....there are no diplomas or graduates...it is continual :lol:

BTW, the TA reading of 0 is incorrect. They either didn't do the test or misread something but you do have some alkalinity in your pool

 

[Guest]

Your water balance is not good. Your CYA is too high and combined with the low pH and TA you reported I assume you are using trichlor in a feeder or floater. This is going to continue to cause you problems. I suggest you click on the Pool School link in the top right of this page or in my signature and read everything to learn how to care for your pool with minimum expense and problems! Then reread the pool school and then post any questions you might have. Also, invest in a decent test kit that includes an FAS-DPD chlorine test (not a DPD test) and start testing your own water.
Your copper levels are also way too high and can lead to black stains on your liner and green hair to those who swim if your pH spikes or you shock the pool. At this point a drain and refill to reduce the CYA and copper followed by regular use of a metal sequesterant to keep the remaining copper from causing problems seems like the way to go.

Sorry if this alarms you but copper over 1 ppm is a red flag!

Have you tested the water for iron? With your low pH that you reported it is entirely possible that you have iron in your water from metal parts of the pool being affected by the low pH (or it could be your fill water also). They type of staining you describe can also be from iron. To test take an ordinary vitamin C tablet and hold it against a stained area for one minute. If the stain disappears in the area of the tablet it's iron and easily treatable. If it does not it's organic and not so easily treatable.
Report back on your results with the vitamin C.

 

[stev32k]

I've been diluting the pool water for several days and believe I've changed about 25% of the volume so far. I've also been keeping the chlorine levels around 10 ppm and raised the TA to 90. The water is good and clear, but the stains are still there.

I do need a good test kit and will order one of the ones I see here.

 

[frustratedpoolmom]

I used to have stains like that - when my water wasn't properly balanced and my CYA was too high (pre-TFP days). After 2 seasons of BBB and proper water chemistry the stains are gone. I did have to run with slightly higher than normal FC for a few months to ensure they were completely gone.

Good luck, we're here to help. (There's an article in Pool School that compares the test kits, I highly recommend the TF-100.)

 

[stev32k]

We've had a LOT of rain the past few days which has diluted the pool water somewhat so I took another sample to the pool store and got the following results:

Free chlorine 6.0
Total chlorine 6.0
Combined chlorine 0
pH 7.5
Hardness 100
Alkalinity 80
Cyanuric acid 90
copper 0.43

It looks like I should continue dumping water until the CYA gets in the 40 - 60 range.

 

[frustratedpoolmom]

It looks like I should continue dumping water until the CYA gets in the 40 - 60 range.

That will also help lower your copper levels.

In the meantime keep that FC above 7 so that you don't get an algae bloom. See the CYA/Chlorine chart.

 

[duraleigh]

Yeah, go ahead and bring it on down. It's simply very difficult to keep a clear pool with CYA that high. When you get it down in the 40-60 range, everything gets easier.

While you're trying to reduce the stains(Which may take another week or more to show any effect), keep your FC up in that 8-10 range even after you get your CYA down. Brush the surface of the stains as often as you have time.....the idea is to expose a fresh "surface" of the stain so the chlorine will keep working on it.

The progress will be pretty slow but I hope you'll see improvement in the next week.

Keep you FC up there! :lol:

 

[Guest]

Have you tried a vitamin C tablet on the stains yet? I am not totally convinced they are organic based on your initial test results.

 

[duraleigh]

I am not totally convinced they are organic based on your initial test results.

Waterbear makes a good point. We are only suggesting high chlorine to treat the stains because it is a sort of passive fix......you don't have to do much you wouldn't do anyway.

Testing with the vitamin C tablet is even more painless and will point to the stains being iron rather than organic.

 

[stev32k]

Have you tried a vitamin C tablet on the stains yet? I am not totally convinced they are organic based on your initial test results.

No, not yet. I don't have any vitamin C tablets in the house and haven't been to the store, but I will in the next day or two.

 

[stev32k]

OK, I did the vitamin C test and the tablet will clean off the stain immediately. I guess that means they are metal stains? Now what?

 

[Guest]

OK, I did the vitamin C test and the tablet will clean off the stain immediately. I guess that means they are metal stains? Now what?

Read this thread on using ascorbic acid to remove iron stians. and if you don't understand something post your question. ascorbic-treatment-to-rid-pool-of-metal-stains-t2298.html

 

[stev32k]

I was reading the article when you posted. The only question I have is about the sequestrant - can Trisodium Phosphate (TSP) be used? I happen to have a box in the garage and it's a pretty good sequestering agent.

 

[Guest]

I was reading the article when you posted. The only question I have is about the sequestrant - can Trisodium Phosphate (TSP) be used? I happen to have a box in the garage and it's a pretty good sequestering agent.

No, you want a HEDP based sequesterant with a high chelation index for iron.

TSP is more effective at chelating calcium (and was actually used for this pupose in pools once upon a time. However, the amount of phosphate that gets introduced into the water can lead to algae blooms since the phosphate levels would be EXTREMELY high and the use of a phospate remover might be mandated also (one of the few instances where a phosphate remover might be needed...better to NOT use the TSP in the first place.)

Also, unless that box in your garage is very very old or you live in one of the very few areas that has not banned phosphates I will bet it is NOT TSP (trisodium phosphate) but rather a TSP substitute such as sodium metasilcate or sodium carbonate since the use of TSP has been restriced or banned in many localities because of the effects of phosphates on the environment. Read the small print on the box and see if it's trisodium phosphate or a TSP substitute. If it says it does't contain phosphorous it is NOT TSP. If it's Red Devil brand TSP it's a substitute. If it's Savogran in the red box it's real TSP, the green box is the substitute.

 

[stev32k]

I was reading the article when you posted. The only question I have is about the sequestrant - can Trisodium Phosphate (TSP) be used? I happen to have a box in the garage and it's a pretty good sequestering agent.

No, you want a HEDP based sequesterant with a high chelation index for iron.

TSP is more effective at chelating calcium (and was actually used for this pupose in pools once upon a time. However, the amount of phosphate that gets introduced into the water can lead to algae blooms since the phosphate levels would be EXTREMELY high and the use of a phospate remover might be mandated also (one of the few instances where a phosphate remover might be needed...better to NOT use the TSP in the first place.)

Also, unless that box in your garage is very very old or you live in one of the very few areas that has not banned phosphates I will bet it is NOT TSP (trisodium phosphate) but rather a TSP substitute such as sodium metasilcate or sodium carbonate since the use of TSP has been restriced or banned in many localities because of the effects of phosphates on the environment. Read the small print on the box and see if it's trisodium phosphate or a TSP substitute. If it says it does't contain phosphorous it is NOT TSP. If it's Red Devil brand TSP it's a substitute. If it's Savogran in the red box it's real TSP, the green box is the substitute.

It is the Savogran brand in the red and white box and is real TSP. As far as I'm aware there is no prohibition against using phosphates around here. Almost every paint store I've been in carries the stuff.

What is "HEDP" I'm not familiar with that FLA.

 

[Guest]

Step into Florida and you won't find and REAL tsp... at any rate, it's not what you want to use.

 

[Guest]

What is "HEDP" I'm not familiar with that FLA.

1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (bet you're sorry you asked now! )
It's the most common phosphonate based sequesterant used in pools and spas. It's found in most of the brands out there like Proteam's Metal Magic and the Jack's Magic line of sequesterants. The other common seqesterant used is EDTA (such as Natural Chemistry's Metal Magic) which is not as effective. However it does not cause orthophosphate levels to rise. However, orthophosphates are seldome a problem in pools unless you dose them with TSP!
If the bottle say it contains HEDP, phosphonic acid derivatives, or phosphonates you have the right stuff. If it says phosphate free you have EDTA and you should place that bottle back on the shelf in the store where you found it!

 

[stev32k]

OK, thanks for the info.

 

[jleslie]

Can anyoone tell me whether there is a maximum amount of ascorbic acid one can add? My pool is 38,000 gallons 16x75 in ground. I've already added 10 pounds and it has only eliminated a fraction of the yellow stains. I'd also like to know how long after adding the ascorbic acid I can reset the water path to flow through the heater. I haven't been able to swim because it has been in the 50's at nightt here in CT.