Calcium chloride question

[congachile]

My calcium chloride turned brown when i added it to bucket of water. First time I used this brand, I bought it from Home Depot. Any ideas?

 

[JamesW]

Maybe dirt, iron, Sodium ferrocyanide (yellow prussiate of soda) etc.

 

[JamesW]

My guess on this is that there are probably brands of calcium increaser that use ferrocyanide salts (calcium- , sodium- , or potassium ferrocyanide) as a flow and anticaking agent. Ferrocyanides undergo reversible redox (reduction/oxidation reaction) -

[Fe(CN)6]4− ⇌ [Fe(CN)6]3− + e−
ferrocyanide ⇌ ferricyanide plus an electron

That electron can be taken up by the chlorine ion (Cl+) in hypochlorous acid and converted to chloride (Cl-). Because of the reversible nature of redox reaction, even trace amounts of ferrocyanide could deplete higher levels of chlorine. The ferrocyanide will break down quickly so it’s not a permanent issue and the amount of iron exposure is insignificant.

 

[JamesW]

A while ago we had a discussion where we observed Calcium Chloride going brown when pre-dissolving in a bucket:

 

[JamesW]

Calcium Hardness - Further Reading

www.troublefreepool.com

 

[congachile]

Thanks so much for your replies, and please excuse my negligence in not replying earlier. I guess I got distracted and forgot about this. Squirrel! I'm inclined to go with the ferrocyanide theory. I have been having trouble keeping my chlorine up, with no other balance issues. Thanks