Hi my name is Tim and I am new to this forum based in Australia. We have a 20k gal salt chlorinated fibreglass heated indoor pool that has brown stains. I was going down the track of it being metals but no metals have shown up in any water testing both before or after removing the stains with ascorbic acid. Since getting the stain off the walls into the water by using ascorbic acid my phosphates went sky high and after a few days the stain is coming back all over the walls of the pool. My question is "Can Phosphates be stored in a stain on the walls of the pool and released when the stain is released into the water? AND if so is it just a matter or removing the phosphates to get rid of the stain."
Brown Stains and Phosphates
- Thread starter HSSS
- Start date
Welcome to TFP!
Phosphates and pool stains are not interrelated. We recommend ignoring phosphates. Iron tests are tricky because you are testing the water for iron, but if the iron is sequestered with a sequestrant or in surface stains then it is not in the water and the test will show 0 even though there are clear indications that iron is present.
If the ascorbic acid treatment quickly removes the stain then your stains are iron. Most iron comes from well water. Occasionally iron is leached into the water by rocks in waterfalls or around the pool. Eliminating from the pool is the only way to prevent stains. You can truck in iron-free water and capture rain water for topping off.
The problem with iron is that it will stay in the water and continue to restain the pool surface forever. AA will remove the stain and put it back in the water and as soon as FC and/or pH rises a bit it will stain again. Or you can use a sequestrant to bind to the iron to prevent it from staining but that will slowly deteriorate and you have to keep adding more sequestrant.
More here, Pool School - Stains in Your Pool
Phosphates and pool stains are not interrelated. We recommend ignoring phosphates. Iron tests are tricky because you are testing the water for iron, but if the iron is sequestered with a sequestrant or in surface stains then it is not in the water and the test will show 0 even though there are clear indications that iron is present.
If the ascorbic acid treatment quickly removes the stain then your stains are iron. Most iron comes from well water. Occasionally iron is leached into the water by rocks in waterfalls or around the pool. Eliminating from the pool is the only way to prevent stains. You can truck in iron-free water and capture rain water for topping off.
The problem with iron is that it will stay in the water and continue to restain the pool surface forever. AA will remove the stain and put it back in the water and as soon as FC and/or pH rises a bit it will stain again. Or you can use a sequestrant to bind to the iron to prevent it from staining but that will slowly deteriorate and you have to keep adding more sequestrant.
More here, Pool School - Stains in Your Pool
- May 23, 2015
- 24,407
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
It is certainly possible for metal phosphates to form (this is how flocs can be used to treat water and remove metals) BUT a metal phosphate would be highly insoluble in water even with ascorbic acid present. Phosphate scale is not something that can be easily removed. Therefore, the stains were most likely metal stains (iron hydroxide and iron oxide) and the AA removed them.
Do you regularly use a metal sequestrant or a calcium scale inhibitor in your pool? If so, those are typically based on HEDP that, when exposed to chlorine, slowly oxidize into orthophosphates (PO4).
How are you testing for phosphates? Do you have a test kit?
Do you regularly use a metal sequestrant or a calcium scale inhibitor in your pool? If so, those are typically based on HEDP that, when exposed to chlorine, slowly oxidize into orthophosphates (PO4).
How are you testing for phosphates? Do you have a test kit?
Hi Folks, Thanks for your thoughts and advice. I only top our pool from town water supply so should not be getting any iron from that source. The water has been tested by two local pool shops as I am unaware here in Australia of a self testing kit for Metals. I do have my own test kit for Phosphates. I have recently used an algicide followed up by a clarifer prior to using the Ascorbic Acid. I was planning to now use Phosphates remover to coagulate these and vacuum out. It sounds like this will not remove the iron from what you are saying. I have read up about the Ascorbic Acid treatment and found that this only puts the metal back into the water and then I need to use a HEDP to cause the metal to form into larger particles that are then captured by a CuLator bag placed in the skimmer boxes. My problem is that both the HEDP and CuLator products are not something any one seems to know about here in Australia. If scale inhibitors are the same as a sequestrant then I have never used one but perhaps that is what I need and I know you can get them here. That just leaves the CuLator to find. I would appreciate any further thoughts you have on this. Cheers
There is one other way to rid your pool of the metals. You aren't going to like it though. Do the AA and then remove most, if not all, of the water from the pool and start over.
Also, just because your water comes from the 'city' doesn't mean it's metal free. How does it get from them to you? And think of this, even if there is only a small amount of iron in the supply water, over time it will build up in your pool.
Also, just because your water comes from the 'city' doesn't mean it's metal free. How does it get from them to you? And think of this, even if there is only a small amount of iron in the supply water, over time it will build up in your pool.
HSS, your "scale inhibitors" may well be HEDP, which DOES break down into orthophosphates over time. With that said, phosphate levels tat you can test with a home kit aren't likely to case you an iota of a problem if you're maintaining TFP level recs.
Yes I think I may be getting small amounts of metals from the town supply and it has built up over time. I have tracked down a stain and scale control agent that is based in a Phosphonic Acid so will do the AA clean again and follow up with the HEDP agent and place some Skimmer socks with Poly filler in them to catch the iron. Hopefully this results in extracting the metals and I do not have to dump all my pool water. Thanks for everyone's help on this and let me know if there are any other words of wisdom.