Yellow pool water after addition of magnesium chloride

[dgoloughlin]

Dear all,

The manufacturer of my salt cell recommends adding 25 kg (55 lb) of magnesium chloride to the pool water each year so that any build-up formed during the process of electrolysis remains soft and mushy, and thus easily removed.

I've done this only for the water to turn yellow.

Is the magnesium reacting with the chlorine in the water or are there contaminants in the magnesium chloride flakes?

It's agricultural grade as the food grade stuff is prohibitively expensive.

Many thanks,
David

 

[Dirk]

Hey David, welcome to TFP. Let's see if we can stump @JoyfulNoise with this one...

 

[JoyfulNoise]

I don’t know why Australia is so fixated on Epsom salt magnesium chloride (thank you @JamesW ) use for chlorine generators ... I guess pool shops can make more money that way since mag chloride is much more expensive than regular sodium chloride. There is no good reason to use mag chloride and all of the “reasoning” I have seen is complete nonsense.

Likely it’s iron contamination as agricultural grades of salts have lots of minerals in them like sodium, potassium, iron, etc.

 

[Dirk]

Thanks Matt!

David, we mostly use sodium chloride here and we control the calcium scale we might get on our SWG plates by monitoring CSI. Most of us don't get any scale, and if we do it either hoses off or we can use a mild acid solution to dissolve it off. We use pool salt, or water softener salt, which is about $7 for 40lbs, and that doesn't cause any contamination. For my pool, that'd be about $130 US.

You could check on Matt's theory by having your water tested for iron, by some place that can, or you can buy a test kit for that. Then decide how you want to handle the result, or check back here to see if someone knows how best to rid your water of the iron. A TFP search revealed a lot of threads about it. Or if water is cheap, maybe replacing it all would be less than a test kit and the sequestrant chemicals. Then you could start over with sodium chloride.

 

[dgoloughlin]

I just wanted to give an update on my little problem.

Before

After


I added some water clarifier (against the forums better advice haha) and have been running the filter 4 hours a day. I also turned off the chlorinator in case the yellowing was the result of chlorine reacting with contaminates in the magnesium chloride.

With the water nearly clear again and with the chlorine at near zero I'll backwash tomorrow then do an ascorbic acid treatment to remove some old stains caused by an earlier episode with dodgy salt.

I found some HEDP based sequestrant (very hard to get here for some reason) which I'll add after turning the chlorinator back on.

Thanks for all your advice I think I've learned my lesson for now. Maybe