Green Pool during Stain Treatment

I was following the instructions in one of Ben's post (which I can't seem to find now) for treating iron stains. Everything was going fine for the first 7 days, but then today the pool turned green. Obviously, something has gone wrong and I'm not sure what it is. Here's what I did:

7 days ago:
(33000 gals, vinyl-lined)
TC = 2
CC = 0
CYA = 50
pH = 7.2
TA = 70
Temp. = 80

Added a full dose of polyquat and waited ~4 hours. Added recommended dose of "Metal Free". Wiped entire pool with Vitamin C tablets enclosed in a mesh bag. I figured this way, it would get the Vitamin C right on the stains and therefore require less. Anyway, the stains lifted off beautifully and the pool was crystal clear.

As expected, CL levels went to 0. Per Ben's instructions I kept the CL level low the entire week, however, I did add bleach sometimes 4 times a day to try to bring it up to around 2.5. Also per Ben's instructions, I added a little Borax to gradually bring the pH up. His instructions said to bring it to 7.8, but I never made it that far, I did get it to 7.6

Day 4:
Notice a slight hint of brown returning to the pool. The wife couldn't see it, but I could. Added what little "Metal Free' I had left (about 1/3 bottle).

Day 7:
Morning: CL equaled 1, so I added 2 gals bleach which in my pool should raise CL by about 3. I figured at this point I could start trying to get the CL up.
Around noon: Checked CL again. Still around 1.5. Added 2 more gals. bleach. Shortly afterwards, the pool started to turn green. Added another dose of Polyquat.

So that's where I am now. The pool is green, and it is still not holding CL. So the question is, what do I do now? And, what did I do wrong? Should I go ahead and start shocking, or will that just cause the stains to return?

Current readings:
TC = 2
CC = .5
CYA = 50
pH = 7.6
TA = 70
Temp. = 83

Of course, any help is most appreciated.

Bobby C.

Sorry for your trouble. First question, did you add enough sequesterant for your pool size? It is always better to add more than enough versus not enough. Second, you may have some algae forming - with a cya of 50 you should not have chlorine under 3 - you need to keep it around 5. The ascorbic acid (vitamin c) will bring the chlorine down to 0, and will continue to bring chlorine down as long as there is ascorbic acid in the water - that's why you bring your chlorine down to 0 efore the stain treatment, because the ascorbic acid gets eaten by chlorine. The bringing the ph up to 7.8 is for trying to get the metals to stain the filter, he wants you to put a trichlor puck in the skimmer basket - this way when the high ph water hits the chorine puck, it makes the metal precipitate out of the water and land on the filter. I don't try to do this myself - I just add the sequesterant and keep my ph low for the first 2 weeks after a stain treatment, so that as I bring up my chlorine levels they are less likely to precipitate the metals. I also keep a chlorine puck in the skimmer. You don't want to put a chlorine puck in the skimmer if you have a cartridge filter - only a sand or DE.

This is what I would do - make sure you have enough sequesterant in the water. Bring your ph down to 7.0 to 7.2. Put a trichlor puck in the skimmer basket and keep your pump running 24/7 (not if you have a cartridge). Add polyquat. Start to bring your chlorine up, and watch for stains (keeping the ph low will help not to stain) If you see stain forming, put more sequesterant in the water. Keep adding more and more chlorine - be consistant - don't let it fall lower than you had it , if you have it at 5 do not let it drop, add more to get it to 7, don't let it drop, keep doing this till you get up to shock levels.
You may have algae, so you will have to get the chlorine up to shock levels, which for you will be 15ppms. It will be hard at first, because the chlorine will get eaten up by the ascorbic acid and the algae. Keep the filter running 24/7, backwash everyday, and if you have a sand filter add a cup of DE to the skimmer, or you can add a skimmer sock (or a cut leg from pantyhose). This will help filter out small particles. Keep us informed, and ask any questions you may have.

Thanks for your reply. I put the recommended dose of Metal Free in and I thought I had enough, but perhaps it wasn't. I will add more. Your advice sounds good, so I will try as you say. Yes, I do have a sand filter. I have already added a whole bottle of Polyquat. Should I add more? How much and when? And one thing I don't quite understand. Why did the pool turn green right after adding chorine? Just coincidence?

You don't need anymore polyquat. Your water may have turned green when you had high ph and added high chlorine. The sequesterant probably kept the metals from falling out onto the surface of the pool. Just a chemical reaction - hopefully you don't have algae, but if you do the chlorine will kill it. The chlorine can also just be getting used up getting rid of the vitamin C. How does the water look today?

It turned from green to crystal clear in about 8 hours! I dropped the pH and I think that made the difference. I also added some more metal out and am adding lots of bleach to bring the CL level up. Looks great now! Thanks for your help.

Bobby C.

Quote:

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Originally Posted by mbar

I just add the sequesterant and keep my ph low for the first 2 weeks after a stain treatment, so that as I bring up my chlorine levels they are less likely to precipitate the metals. I also keep a chlorine puck in the skimmer.

This is what I would do - make sure you have enough sequesterant in the water. Bring your ph down to 7.0 to 7.2. Put a trichlor puck in the skimmer basket and keep your pump running 24/7 (not if you have a cartridge). Add polyquat. Start to bring your chlorine up, and watch for stains (keeping the ph low will help not to stain) If you see stain forming, put more sequesterant in the water. Keep adding more and more chlorine - be consistant - don't let it fall lower than you had it , if you have it at 5 do not let it drop, add more to get it to 7, don't let it drop, keep doing this till you get up to shock levels.

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So how does the metal actually "get out of the water" with this process? Does the sequesterant (I'm assuming Metal Free) make the metal "filterable"?

Sorry, but the metal stays in the water. The sequestering agent bonds to the metal and keeps it from precipitating out. So far I know of no way that takes the metal out once and for all. That's why it is important to keep enough sequestering agent in your water at all times. I am still researching.

Quote:

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Originally Posted by mbar

Sorry, but the metal stays in the water. The sequestering agent bonds to the metal and keeps it from precipitating out. So far I know of no way that takes the metal out once and for all. That's why it is important to keep enough sequestering agent in your water at all times. I am still researching.

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Hmmm... can shocking force the iron out of the sequestering agent and back on the liner? That would really be bad...

Quote:

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The bringing the ph up to 7.8 is for trying to get the metals to stain the filter, he wants you to put a trichlor puck in the skimmer basket - this way when the high ph water hits the chorine puck, it makes the metal precipitate out of the water and land on the filter.

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I understand this to mean that the high chlorine in the puck makes the metal precipitate and stain the DE in the filter, The backwashing would then flush the DE and the metal along with it, removing it from the pool.

.

leejp, yes shocking espeically with high ph will make metals that are not bound by sequestering agent precipitate out and stain the liner.

haze1956,
Yes, one way to get the metal out of the pool is to put a trichlor puck in the skimmer basket and raise your ph up to 7.8 - this will make metals fall out on the filter, which will then be backwashed out, therefore it will get the metal out of the water - the only thing it could also stain on the pool - that's why I like to use the method of sequestering the metals, but the metals do not get filtered out. I also like to put a puck in the skimmer when I am first bringing my chorine up after a stain treatment to make sure if I don't have enough sequestering agent the stain will hopefully fall out on the filter first. I do not raise my ph when doing this - I keep it at about 7.2.

Hi Marie,

I'm curious to understand how this metal removal process works.

Is it high PH or the high chlorine of the Trichlor that makes the metals precipitate?

And if the filter fails to catch the metals and they return to the pool, would they stain the liner or would they go back into solution as the filter water dilutes in the low chorine, low PH, pool water?

.

I know it is hard to get a handle on it - it took me a while. This is how I think it goes:

High chlorine along with high ph causes metals that are in solution in the pool to fall out and stain the pool.
Sequestering agent binds with the metals in the water so that they stay in solution and do not fall out even with high chlorine and high ph. The problem is, they don't ever get filtered out. They just stay in solution, so you have to keep enough sequesterant in the water at all times.

If you see stain starting to form, take your ph back down to 7 - 7.2 and add more sequesterant - this will most likely lift the stain if it just occured. The lower ph helps to keep the metals in solution - what you use to take metals off the surface of the pool is ascorbic acid - low ph means your pool is acidic. It is when the ph is high and the chlorine is high that they react to separate the metals from the water and they land on the pool, or if you can do it right, you can get them to land on the filter and they WILL get filtered out, but it is very hard to do - therefore I opt to go with the sequesterant. I never tried the method, so I don't know, but my guess would be that it is more likely that if the filter fails to catch the metals, the stains will end up on the surface of the pool after awhile.

This was the long answer, the short answer is that it is the combination of the high ph along with high chlorine (trichlor puck in skimmer) that make metals fall out of the water. I got carried away!

Quote:

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Originally Posted by mbar

leejp, yes shocking espeically with high ph will make metals that are not bound by sequestering agent precipitate out and stain the liner.

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This IS complicated...

How long is the metal "bound" to the sequestering agent? Probably not forever, so I now have a maintenance routine for stain control unless I drain and refill ;(

What's the difference between a sequestering agent and a chelating agent?

Thanks Marie,

I appreciate the information,

I can see how the metals could be removed if one really wants them gone, but not sure how fast that could be done.

It would be an interesting experiment though !

.

I don't know how long the metal stays bound to the sequestering agent, maybe waterbear can answer that one. I do know that you have to add a sequestering agent when you add a lot of fill water, on the bottle it says to add a weekly dosage, but I only add the sequestering agent when there is a lot of new water in the pool, or I see some stains starting to form.

I am still trying to find a way to take the metals out of the water that's not too hard or expensive. I know there are ways - but I don't know any that are easy enough to make it worth it for swimming pools. You can drain and refill, but you have to find a water source that doesn't have metal. I have a well, so I just deal with it. I keep researching......