Best way to lower Iron in a pool

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EnoughToBeDangerous

0
Gold Supporter
Oct 4, 2018
89
Long Island, NY
Pool Size
25000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Autopilot Digital PPC1 (RC-35)
After enjoying several seasons of trouble free pool using the methods on this forum, I'm having a problem with Iron that I can't seem to overcome. My iron test strips show that there is no iron in the municipal water or in the pool water, but that is clearly not true. Last season I started having an issue with iron deposits on the liner. I removed with ascorbic acid, used sequestrant, and also used a CUlater. It held up okay, but it seemed to get worse over time. This spring when I opened about 3-4 weeks ago, the stains were back in force. I used the AA treatment to dissolve the stains, then I performed a water exchange, which managed to remove about 50% of the salt in the pool according to my test kit. I resalted the pool, and balanced the chemicals, though the ph remained on the low side, around 7.0 occasionally drifting below 7, chlorine demand was high. A week ago I added some washing soda, to bring it up a bit. Last night I saw a totally clear pool, and a pH around 7. This morning I noticed the iron stains coming back, the pH had jumped to 7.8. My first thought is the AA finally had broken down. But it's difficult to keep the pH from ever going up to 7.8 for an entire season, there must be too much iron still in the water. I didn't have muriatic acid on hand, but I did have some dry acid which I added to quickly bring it down.

pH - 7.3
TA - 70
CYA - 30
FC - 3
CH - not tested

Solutions from TFP I've considered:

-Drain and fill: This did not seem to do the trick, because I cannot drain the pool completely since it is a vinyl liner pool, and it seems likely there is iron in my fill water.
-Reverse osmosis: I cannot find a provider in my area.
-Truck in water: Seems not very practical since I cannot drain the entire pool.
-Precipitate and filter out: Some have had success, but only with visible iron in the pool. If I precipitate the iron by raising the pH and chlorine, much will likely stick to my liner. Could this work?
-Specialized filters, such as green sand filters, it seems difficult to accomplish on a large scale, concerns about manganese contamination appear in the wiki.
-Precipitate and floc: Floc is not popular on the TFP forum. However a number of sources suggest a common strategy is to precipitate the iron and then use floc to sink it and vacuum it to waste. Seems plausible this could help.

What do you think I should try?
 
The force iron to precipitate then attempt to remove it mechanically option (whether it be polyfill or other means) is a risk because theres no way to know how much staining you’ll endure. The precipitation generally just happens to people then we suggest attempting mechanical removal. Its not generally recommended to force it to happen because of the staining risks. But you do know how to handle those.
If you’re like me you may have just enough iron to stain but it never precipitates out even at mustard algae slam levels.
Couple of questions:
Did you add more salt after your water exchange?
What brand of salt do you use?
What sequestrant did you use?
Did you do maintenance doses of sequesterant?
 
Thanks for your reply. In response to your questions:
I did add more salt to the pool. The brand I'm using is Diamond. I used Jack's Purple. In the past I've used Metal Out. Yes I did do maintenance doses, if I used even more, perhaps it would work better, but at some point it gets to be unpractical.
 
Ok well, I was organizing my pool supplies and there was an old bag of salt from three seasons ago. Yep, it was chlorox. And right around that time is when I started having this iron problem. I guess what I need to focus on now is finding a more effective way to exchange my water.
 
We like the no drain exchange method. Outlined in draining further reading.
Its the safest option for most people.
You can do a little of both. Sequester now then replace water when you’re ready.
If you didn’t replace all the water you will likely still need some sequestrant.
Any future water replacement will mean further dilution which is helpful if you pretty sure it was the salt.

Metals testing is the only test that we recommend you go to the pool store for so you may want to check what they say your iron & copper levels are for both pool & fill water. Just to get another metric.
They aren’t necessarily the most accurate either but moreso than what a homeowner usually has access to at a reasonable cost.
 
Mdragger88 said:
Yes, it does.
Did you test your fill water?
Click to expand...
I did the bucket test method described in another post on this forum. I filled a bucket with my fill water, added a large amount of bleach, and observed the color after 1 hour. It did not turn yellow or brown. I'll consider having it lab tested if I can find a practical way to do that. The water authority reports show very low iron content.
 
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