Green Pool during Stain Treatment

[haze_1956]

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?

.

[mbar]

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!

[leejp]

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

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?

[haze_1956]

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 !

.

[mbar]

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......