Newbie just beginning to understand "free" and "total" chlorine. . .

[Hainsworth]

Update: My initial "green water" issue resolved itself after several days filtration. I did shock with bleach and deicded to use a borate buffer as is recommended on so many posts regarding SWCG pools. Hoping I can get to a nice equilibrium at 7.7 or 7.8 and avoid the drift with less carbonate alk.

Todays numbers from my Taylor K-2006:
FC 6
CC 0
pH 7.8
Hard 280
Alk (carb) 90
CYA 75-80

But the plot thickens!! After your earlier posts, I tested both the pool and my fill water (hydrant on well) for copper and iron (because those are the test kits I have ) and came up nada on both. I thought I was good to go . . . until I had to put the hose in the pool again this morning and now have (drumroll) slightly greenish water! The goos news, I think I know what it might be - I just need to know what you all think. My well is acidic (about 4.9) so we installed an acid neutralizer for the house to save our fixtures and keep my from constantly scrubbing off the copper stains! These us Calcite (calcium carbonate) in a tank just like a water softner, but the goal is to raise the pH. However, because our pH was so low, we needed a mixed media, 90% calcite and 10% corosex which is magnesium oxide. Could that Magnesium be reacting with the pool water (chlorine) and causing the green tint? I can bypass the neutralizer (what a pain), and plan to in the future for adding water, so I will see what happens next time. What do you think?

Thanks again. Your site had been invaluable to me and I am so pleased to have such a beautiful (albeit currently slight green) pool that I now truly understand!!

[aylad]

Yup, magnesium reacts with the chlorine in the pool water, just like iron and copper do. Good work!!

Janet

[waterbear]

I have never known magensium to turn water green but wonder if you might have any copper or brass plumbing on your well? That could explain the green water (acidic water going through the metal pipes or fittings).
If you have used a 'metal out' product (seqeustrant) then it is entirely possible that your water would test negative for metal even when they are present (but sequestered).

[Hainsworth]

Thanks Janet and Waterbear,

There is no copper on the well line or on the way our to the hydrant, there are probably two brass fittings between the well and the fill hydrant, but certainly not enough to cause discoloration in fill water, especially now that the incoming ph has been corrected to darn near 7.0.

The neutralizer media is 10% magnesium oxide which combines with water to form magnesium hydroxide (a base) thus raising the pH of my incoming acidic water. My research says that magnesium hydroxide combines with chlorine to form magnesium chloride (a salt) which I think shouldn't be a problem in the pool, but also isn't doing any work for me either . Unless my SWGC can break it down too, but I have no idea. . . .

The (again VERY slight) coloration to the water goes away with 2 to 3 days normal filter operation after a fill. It really only got my attention because we didn't have anything like it last year (first year for pool) . . . but that was BEFORE we got the neutralizer up and running. So, ironically, last year we were much more likely to have been adding some trace metals since we were adding pH 4.9 fill water that was surely leaching stuff from my hydrant, etc.! I'm thinking that the slight color cast after a fill is the effect of the magnesium compounds going through their changes when they hit the chlorine, and that after 2-3 days they're all magnesium chloride and the color cast is gone. I plan on bypassing the neutralizer the next time I need to fill and see what happens, if nothing, I'll assume I'm right.

In the meantime, I've added a borate buffer and am lowering my carbonate alk (per your instructions on the forum) to try and stabilize my pH - it was always creeping up as I (now) understand is normal for a SWCG system.

I do know why it happens, but I still can't believe that a pool company would sell you a system and not teach you the hows and whys of it's operation. That makes me nuts! So grateful to have found your forum so early in my days of pool ownership . . .Thanks all!

[aylad]

I do know why it happens, but I still can't believe that a pool company would sell you a system and not teach you the hows and whys of it's operation. That makes me nuts! So grateful to have found your forum so early in my days of pool ownership . . .Thanks all!

I find that most folks that work in a lot of the pool companies (at least around here) don't actually own pools, and if you've never actually used a product yourself, you don't know the hows and whys, either. Just about anybody can read a set of instructions for a product and tell you what it's "supposed" to do, but having folks who actually have practiced what they preach makes all the difference. I'm still waiting for ANYBODY to report that a salesman who sold them an Intex pool warned them that metals from well water could be an issue for them!!

Janet

[BigDave]

If you do bypass and add pH 4.9 water to your pool, be sure to have plenty of Borax on hand.

[Hainsworth]

Thanks BigDave!

Will do. Intereseting to note that last year, when all fill was 4.9, we never had a pH reading below 7.7. I guess that a little bit of 4.9 made up for the SWCG pH creep. I'm only using "fill water" for incedental loss due to splash out or evaporation when it's dry so it's not too much (fow now). Didn't need any fill at opening because mother nature did if for me over the winter , and it opened at 7.5!