Hi there. I'm new to this forum. It certainly seems to be the best one around after spening a lot of time trying to get a sensible answer from other sites.

Here is my problem, a brief history of what I have discovered and what I think is wrong. I'm really hoping I have come to the wrong conclusion.....

Problem: A light brown stain that is even all over the floor and walls of my fibreglass swimming pool - anywhere the water touches. It is like a plating has occured. No scrubbing removes it (so probably not algea), no 'miracle product' has had any impact. There are nometal pipes or otherwise touching the water. I've been good with keeping within recommended chemical levels.

A brief history: The only thing that moved the stain was a 15% dilution of hydrochloric acid. No elbow grease needed, just washed off. Excellent. So I put 20 litres (5.2 US gallons) in my 36,000 litre (8,000 US gallon) pool and after a couple of days on recirculate the pool looked as clean as it ever has. Excellent. Of course the balance was now wrecked so I slowly bought up the levels and made sure my Total Alkilinity, PH, hardness, sunblock were at optimum levels and only then added the chlorine. By this time algea was forming so I also added some polymeric algeacide (non copper based).

Within 24 hours the pool went brown again. Not excellent. My levels are as follows (as accurate as test strips can be):
pH 7.2
TA 120ppm
free chlorine just below 10ppm
Hardness was tested at pool shop and okay, cyanuric acid a little high but not enough to cause an issue.

It is only the pool that is discoloured. I put a plastic milk container (it is a white colour) half in the water and this didn't go brown. If I rub the stain with ascorbic acid the stain comes off.

Answer??? Has the fibreglass just reached the end of it's life and has just become reactive to the water?

Any help would be great. I'm going nuts here and I don't want to keep spending money on a more fundamental problem.

Thanks anyone who can help.
Koos

Sounds like iron staining. High ph, it starts precipitating out, low pH it dissolves back into solution. The ascorbic acid test seems to confirm it.

A metal sequestrant seems to be in order. Or you can be another test case for the CuLator culator-ready-to-test-t33989.html

What exactly does the cyanuric acid a little high but not an issue mean?

Did they bother to tell you what it was? We can't answer your question about the FC level without knowing that number. High, to a pool store could be anything between 50 and 300. What's too high to them?

I can't comment about the staining, but I did want to ask for your CH, CYA, and TC results if you have them.

X2 on what Richard said...

Thanks for the replies so far.

FC (free chlorine?) = between 5 and 10 ppm (i'm using a test strip at home)
CYA (CYANURIC ACID?) = 160 (was 181 until I got the TA and pH correct)
CH (CALCIUM HARDNESS) = 103

I have tried a metal sequestrant a while back and it didn't help at all (can't remember the product though)

If it is iron stain where does the iron come from. If I lower the pH won't my pool become more acidic and be less efficient for the chlorine? But I'm willing to try anything. I have some pH down.

Could it be the fibreglass? (pool was here when we moved in and I'm guessing it is between 15 and 20 years old)

Many thanks
Koos

Ooh, and forgot to say. In the last proper test I had done the Iron reading was N/T (no trace I assume), copper n/t, manganese n/t. But I have subsequently got my ph, Ta and chlorine to recommended levels.

For a CYA 160 pool, your minimum FC is 12ppm, high target (nightly dose) is 19ppm. Maintaining 5-10 (wide range there, is it 5, or is it 10?) is far to low for your estimated CYA value of 160.

Now, with that being said the strips you're using are very inaccurate and you should not adjust your pool according to their results. I've used strips, and I've used a FAS-DPD test kit. At the same time. The strips are junk, so far off from the actual values it isn't even funny.

Additionally, pH and TA have nothing to do with CYA values. Absolutely nothing. It sounds like you're getting your results from a pool store, which are notorious for being all across the board inaccurate (although better than a strip). I know this sounds like a route statement but there are far too many members here who have compared their own test results with the pool stores to discount this fact. Testing your own water with a quality kit allows you to adjust your pool properly, the ride to the pool store itself can change the water's values. Testing poolside is the only way to get accurate results.

So we're all going to recommend that you get a test kit, and it should be a FAS-DPD kit. Our favorite kit around here is the TF100 found at http://tftestkits.net. It's the best value for your dollar, and sold by wonderful people who care about your pool. Shipping is mega fast as well. We don't get anything for recommending the kit, it is simply a great value for the one essential tool you need to care for your pool.

Chlorine is actually more efficient at lower pH levels. So when you're recommended to lower the pH to stop the iron from staining (high pH allows it to stain, it just is...) do what is recommended. If you're worried about chlorine, worry that you do not have nearly enough in the pool at any given time to effectively disinfect it, the pH affecting it's effectiveness is fairly low in importance compared to the CYA affecting it's ability to do it's job.

The ascorbic acid treatment requires low/0 chlorine from what I've heard. It may be better to deal with an algae issues you may have before you do the treatment.

Hi Frogabog. Thanks for your input. I need a little while to make sure I comprehend all of this. I'm quite new to the process. I'm also in NZ so I will see if there is a supplier for the test kit, if not I'll look at getting one shipped. I understand your approach to fresh testing.

In your opinion, can I count out the problem coming from the fibreglass pool itself?

Where do you think my pH level should be for the stain to lift out? I was recommended 7.2 to be kind on the fibreglass but keep within a recommended range.

I would not blame the pool surface just yet. The water is the problem.

Those who have suggested you lower the pH have done so because it can help. Do that. No one here has any reason to steer you wrong, we make no money off of doing so (like the pool stores do).

As far as the kit... talk to http://TFTestkits.net before you give up. There may be an option for you, or they can help you find what you need.

So I'm slowly adding pH down and keeping the chlorine up. I'll see what happens over the next few days......

It's not unusual for the pool stores to test negative for metals when they've deposited on the surface.

How do you fill your pool?

Read Pool School on how to do the Ascorbic Acid Treatment and follow it. Sequestrant immediately after the treatment is the key to keep it from redepositing. You'll have to add weekly maintenance doses of it too.

I just want to make it absolutely clear that your pool surface is not the problem; you have iron in the water, regardless of what the pool store tells you.

That n/t means "not tested". So you really have no idea what those levels are.

Okay, getting a test for iron on Friday. Been slowly adding pH down (150grams per day) and a sequestrant, keeping chlorine low too but not seeing any difference yet. Struggling to find a supplier of ascorbic acid in NZ.....

Daft question but where does the iron come from? As far as I know all my piping is PVC. I installed a new pump and filter recently. We do get a lot of rain but when dry I top up with tap water (not more than 3-5% in total volume though).

I'm ordering a decent test kit as well.

Thanks for the input so far. I'll update shortly with more accurate levels.

Thanks for the help so far. (I'm feeling good that it is fixable!)

It's fairly common to find iron occuring naturally in water.

If you can't find ascorbic acid, citric acid or oxalic acid will work as well (slightly larger amounts required). I don't know if those will be any easier to find, but there ya go. In the US many people use citric acid as it is usually quite a bit cheaper than ascorbic.

Quick update.

Cannot find ascorbic acid in New Zealand. Will keep trying though.

I've been trying to bring down my Ta and Ph TO SEE IF THE STAIN LIFTS. cURRENT LEVELS ARE

Ta 165
pH 7.2
Chlorine 2.5
CYN 162
Hardness 200

I'm, concerned that the CYN level is high, is there a way to bring it down other than dumping water and refilling (with the potential of iron in the tap water?)

My pool guy didn't have the reagent for testing for iron, he's going to try and get some. He hasn't seen iron issues for over a decade so doesn't stock it.

I'm going to slowly lower to a pH of 6.6 and Ta of 120 and see if the water clears a bit. I'm worried about algae but I have some polymeric in there to keep it at bay. I'm going to keep the chlorine low too.

Here is a concern though. If my pool is plating because of iron content, why does my skimmer basket not stain (white plastic) nor does the white plastic bottle I have half submerged as an experiment. Is it a possibility it is the gel coat reacting.....?

Thanks for any thought. Getting frustrated.

If CYN is cyanuric acid then 162 is way too high and there are only two reliable ways to lower it. Reverse/Osmosis or dumping water and refilling.

The iron will stain the fiberglass much easier than it will stain plastic. Especially under certain conditions.

Thanks Bama. I'm not keen on dumping too much water as I will have to refill and the iron may be coming from the tap water. How do you do reverse osmosis?? Sounds intruiging.

Thanks

There are several places around the country that perform reverse osmosis filtering on pools. If you're lucky enough to be in one of the service areas, it's worth looking into. Since your fill water has iron it's definitely worth looking into. It'll remove the iron too.