Baking soda turned my pool green

[BigStein]

As the day goes on and I continue to bring my ph up with Borax, my pool water has lost off the green color and is currently a cloudy blue (which is clearing), I am wondering if I even need to add all this Magnet Plus stuff? From what I can find, the metals pretty much only seem to be an issue when they turn your pool green or stain your liner, neither of which has happened to me before this. Given that the pool is no longer green perhaps I can just let the copper sit and deal with it if and when it reappears?

On the fence here, I am pretty sure that the green was caused by some kind of reaction from copper when I put all the baking soda in, but if it goes back to being clear now I am not sure if I need to put these chemicals into the pool. I will certainly know to raise my TA more slowly next time either way.

[chem geek]

Copper carbonate is blue-green and not very soluble in water (solubility product of 1.4x10^-10) so in a pool with 100 ppm TA, 30 ppm CYA and pH of 7.5, the carbonate is 3.9x10^-6 moles/liter so that means you can have up to 1.4x10^-10/3.9x10^-6 = 3.6x10^-5 moles/liter of copper which is 2.3 ppm.

So you are at the "edge" of precipitating copper carbonate and the addition of the baking soda created a locally high level of carbonate until it more fully dispersed. Basically, if your pool's pH rises, then you will very likely get the blue-green tint again. So I suggest using a metal sequestrant.

Another compound is copper hydroxide which is bluish. It's solubility product is 2.2x10^-20 (other sources say 4.8x10^-20) and the pool water as described above has hydroxide concentration of 5.3x10^-7 moles/liter so theoretically this is even more likely to precipitate, but in practice it looks like it doesn't (for reasons I do not know).

Richard

[BigStein]

Richard, thanks for the part in bold and where you say 2.3ppm, as moles per liter are well beyond my education level.

I will be adding the sequestrant as soon as my chloring level drops below 1.

Again, thanks for all the help. This place is great, even if I can't convince my other pool owning friends to hop on board (and believe me, we argue about it constantly).

[BigStein]

I did have another question, now that I think of it. After I add the sequestrant will future tests still indicate the presence of the copper? I am guessing that it should not or they will want me to treat it every time I get my water tested (although I think I will get my own metal test now).