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).

[mbar]

Pool manet is a sequestering agent. It sounds like you got copper in your water somewhere - I hope not from your heater coils Your pool has been very acidic, which would keep the copper in suspension. You then added all the baking soda, which caused the copper to precipitate into the water. High ph, alkalinity, calcium added to chlorine could precipitate metals out of suspension. You can add the sequestering agent - you don't have to wait for the chlorine to drop down. You are probably just on the brink of the metals precipitating out, and the sequestering agent will keep them in suspension. All I would do is add the sequestering agent, the chlorine will use some of the sequestering agent up, that's why they want your chlorine down, but not fast enough to do harm - I would think letting your chlorine down will be worse, giving you more of a chance to get algae again. So, add sequestering agent - wait about two hours, then add borax - it will be hard to get the ph up, because the sequestering agent will take your ph down, and use up chlorine- so you will have to test often, taking the ph back up (only to 7.2 for now), and adding bleach to take it back up to 5 each time you test. Your water should clear with your pump running 24/7. You can add the sparkle up - it is just cellulose to coat the top of the filter to filter out small particles - so it will help clear the water. I never heard of anything that really gets metal out once it is in the water, so I don't know if I believe that sparkle up will do it As long as there is enough sequestering agent in the water, your water will not test possitive for metals. You will have to add sequestering agent any time you see the metals start to precipitate out into the water(not a big deal). I think your water will be blue and clear in no time Your alkalinity is fine where it is. Keep us informed

[chem geek]

I believe that the metal test won't show the metals if they are sequestered. The metal tests are expensive. The Taylor K-1264 Copper and Iron test is $83.95, though the K-1730 copper test is only $21.05 but only measures to 1.0 ppm. The Taylor K-1738 measures copper up to 3 ppm and is $49.65 so this latter test is probably the one to get, if you get any.

Waterbear might know of better tests and would also know if the metal tests will show sequestered metal.

Richard

[BigStein]

Again, thanks for the input. My chlorine was down to about 2 or 3 this morning when I tested but after reading your post I put the Magnet stuff in. The water was pretty clear before I put it in except for a film on top (not sure if that is part of the copper reaction or what) so it should look good in no time.

On the plus side, I have been taking ph readings and adding Borax slowly while waiting for the chlorine to drop and had my ph up to 7.2 this morning, so had a good start point before putting in the magnet.

As for where the copper came from, it sounds like I have not been doing my heat pump and favors with my ph and TA but tests earlier this season were fine so the drop is relatively recent (from not testing enough I fully admit, an error that will not be repeated by me), but I do use well water to top off so that could be a source as well.

I had actually looked up the Sparkle Up too, and don't see how it would take any metal out, but seems like an interesting thing to add to the DE once or twice a season to really get the water clean.

Thanks again and I will keep everyone informed of how things go, and I will likely be taking another water sample to the pool store to test after a week or so to see how the copper number comes out.

[BigStein]

The water is now clear as ever, I will continue to adjust for ph until I hit 7.2. Again, thanks to all for the help.