Question about recurring "metal" staining

[daronj]

My pool is about 2 1/2 years old and I keep getting recurring staining that I believe is metal. It's a brownish staining that begins showing up on the plastic parts (skimmer baskets, returns, etc.) and then starts tinting my pool walls brownish. I add 2 lbs of ascorbic acid and in about 30 minutes it's clean as a whistle. The problem is that metals never show up in the tests from the local pool store. I have tested it when clean and when the staining was present. I keep adding sequestering agents and weekly maintenance doses, but the staining keeps returning after a month or two which requires another ascorbic acid treatment. Anyone have any advice on what is going on? My pool store doesn't.

Here is my latest water chem.

FC = 2
TC = 2
PH = 8
TA = 100
CYA = 35
Calcium Hardness = 200
Salt = 3100
Phosphates = 400

 

[linen]

Welcome to tfp, daronj

If you haven't read it already, a good starting point would be this pool school article: http://www.troublefreepool.com/pool-school/metal stains

Additionally this thread may also be useful, it is about the ascorbic acid treatment, but near the end of the post it discusses keeping ph low combined with adding more sequestrant if the stains keep showing up: http://www.troublefreepool.com/ascorbic-treatment-to-rid-pool-of-metal-stains-t2298.html#p17716

Hopefully others (with more direct experience than I) will chime in also.

 

[JasonLion]

Welcome to TFP!

It is fairly common for the metal tests to read zero even when there is enough metal in the water to cause stains. None of the pool store chemical tests are all that reliable, and the metals test is one of the most likely to be wrong.

When you remove the stains with ascorbic acid, the metals go into the water, instead of staying on the pool surface. Unless you add sequestrant regularly, the metals will simply redeposit on the walls. Sequestrant binds to the metals and prevents them from forming stains. Unfortunately, sequestrant breaks down slowly and needs to be replenished regularly (typically weekly). The only completely reliable way to remove the metals permanently is to replace water with water known not to contain metals.

One factor which greatly increases the odds of stains forming is allowing the PH to get too high. You list your PH as 8, which is too high and will encourage stains to form. When you are having metal stain issues it is important to keep the PH at 7.8 or lower at all times, and if practical, at 7.6 or lower.

 

[daronj]

Okay, thanks for the info. I have obviously been getting bad advice. I was told repeatedly that adding the sequestering agent would cause the metals to be removed by the filter. How can I tell how much I need to add weekly? I have tried adding weekly as per the instructions but still got some staining. I guess it may be a trial and error thing until I get it under control.

Thanks-

 

[JasonLion]

I was told repeatedly that adding the sequestering agent would cause the metals to be removed by the filter.

That does happen now and then, but not nearly often enough to be able to count on it happening.

By the by we don't recommend using Metal Free. Sequestrants based on HEDP, phosphonic acid, or phosphonic acid derivatives are the most effective. ProTeam's Metal Magic and Jack's Magic The Pink Stuff (regular), The Blue Stuff (fresh plaster), and The Purple Stuff (salt) are some of the top sequestrants. You can also find many other brands with similar active ingredients, some of which are noticeably less expensive.

There is a sequestrant test kit you can get to help you figure out dosages of sequestrant, but many people go by trial and error.

 

[daronj]

Thank you for the advice. I have been using Metal Free, but will change to the Magic Jacks and keep on top of the weekly maintenance dose. The assistance is appreciated.

Daron

 

[keene3b07]

Is a product called resist from applied biochemists a worthwhile sequestrant?

 

[yeggim]

Is a product called resist from applied biochemists a worthwhile sequestrant?

Looks like the sequestering agent in that particular product is Sodium Citrate. I'd stick with the brands that JasonLion suggests.

 

[smallpooldad]

It seems to be generally agreed that there are two main reasons for iron stains re-occurring, one is a pH above 7.4 and the other is an insufficient reserve of sequestrant.

In the case of Jack's Magic Purple Stuff, a phosphonic acid based sequestrant, the minimum would be 10 ppm, however I have found the greatest success when I have 40 ppm. You would need to purchase Jack's Test Kit to monitor your concentration or you are "Walking in the Dark."

When I kept it at the minimum level, of 10 ppm stains would slowly reappear after a few weeks, at 20 ppm after a few months, but at 40 ppm it is nearly stain free after 5 months. We have a lot of brown volcanic iron blown dust into the pool, at certain times of the year our winds can blow at 35 to 50 mph for a week or so. When this happens I test the sequestrant twice a week, or more.

When doing an ascorbic acid clean in my 10,000 gal pool I find it eats up about 8 - 10 ppm of sequestrant.

If you do not have an automatic ph/Acid metering system I have found that keeping the pH at 7.3 allows for a margin of error.

What kit are you testing your balance with? This site has an excellent test kit by all accounts, as does Taylor Industries. If you are using another your figures could be off, if your chemicals are out-of-date the measurement could be wrong, by calling Taylor Industries with the code on the bottle they will let you know if they are still usable. Generally speaking I would not trust a pool store's results, especially if they use and electronic readout machine as these are quite difficult to calibrate correctly. My own experience with those machines has been far off the true numbers.

In addition, and I do not know why, that by keeping the CyA between 70 and 80 as recommended by this site, and the Chlorine at 4-6, this to helps keep the stains away. Again I do not know why but it does.

My personal numbers look like this:

Cl 5 -6
pH 7.3 -7.4
TA 80 - 90 (does not budge)
CH 375
CyA 70-80
Salt 3300
Borates 0 (dog)
Temp 72F

Phosphates are well over 20,000 ppb but they are no trouble so long the Chlorine is kept at 5 or above (max 9) or you will have problems getting a pH reading.

Hope this helps and Good Luck.

 

[JasonLion]

In the case of Jack's Magic Purple Stuff, a phosphonic acid based sequestrant, the minimum would be 10 ppm, however I have found the greatest success when I have 40 ppm.

Both of these numbers depend on the amount of iron in the water, so 10 ppm and 40 ppm will not generally be correct for other pools.

In addition, and I do not know why, that by keeping the CyA between 70 and 80 as recommended by this site, and the Chlorine at 4-6, this to helps keep the stains away. Again I do not know why but it does.

Because it minimizes the PH variation when using a SWG. This of course only applies when you are using a SWG, both recommendations are different if you don't have a SWG, see Pool School.

 

[smallpooldad]

Jason is of course correct when he states this "CyA between 70 and 80" only applies to SWG pools which your is. If you do increase your CyA to the 70 to 80 range then you will have to up your chlorine to a minimum of around 4.

As regards the following statement I wrote:

"In the case of Jack's Magic Purple Stuff, a phosphonic acid based sequestrant, the minimum would be 10 ppm, however I have found the greatest success when I have 40 ppm."

The minimum level Jack's tech team recommended to me was 10 ppm, when I called a year or two ago. As far as increasing the base level amount, as I have done, based on Jason's comment you might want to start at 10 ppm and increase to the point where you have little or no staining as I have done. Over 40 ppm does not for me at least seem to have any additional benefit and we do get a lot of wind born iron as mentioned. If you do get iron in only your fill water then a minimum or slightly higher level might apply.

Interestingly when I spoke with Jack's tech team they did state doubling the 10 ppm might help and even going as far as doubling that if I still had trouble which I did to get to 40 ppm.

Hope this helps.