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Muriatic acid turned green

I put muriatic acid [affil links] into a small glass jar (to make it easier to handle than a gallon), and overnight it turned green. What happened? Is it still good for using in swimming pools?

Brian Bagheri
- Alachua, Florida
2002

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Brian.. just a guess here.. but I would imagine the fumes attacked the lid of the jar..there-by, discoloring the solution. As to whether its ok to use.. I would imagine so..but I'm not a swimming pool expert.

Marc Green
anodizer - Boise, Idaho
2002

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I agree with Marc. Here in the UK we don't need swimming pools - firstly it is too cold and secondly it always rains! Seriously, I would also expect the green to come from the container. Muriatic acid is hydrochloric acid and this is quite capable of dissolving many different metals, including iron, chromium and nickel, all of which will turn the liquid green. If the top has a mixture of these metals on it, once the acid has got through any pores in the top layer, you have a great galvanic couple that will promote further dissolution. I suppose it is possible that the acid has begun to decompose and give off chlorine by the action of light, but that isn't very likely. I have seen a similar thing in the past, but that was over a much longer period (months). As far as using it in a pool, ask an expert on pools.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2002

I maintain my own pool and use muriatic, or hydrochloric acid to lower the ph of water as necessary. It is sold at pool service centers for that reason.

Mark Yeats
- Corpus Christi, Texas
2004