scale build up on inground pool

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craftylym

scale build up on inground pool

Postby craftylym » Fri 02 May, 2008 06:45

We have an in ground pool that is crystal clear, but over the winter the walls steps and swim outs are now coated with a salt like covering which I was told are calcium deposits. We have city water.
We tried brushing them with a wire pool brush, used 4 quarts of a chemical that is supposed to dissolve this "stuff", but it didn't do anything.
We do not want to drain the pool, and were told that we should put 16 gallons of muratic acid into the pool, run the filter for two weeks, brushing the pool walls and floor twice a day. The pool holds 11,500 gallons of water.
Does this sound like a good idea? I am just afraid of damaging a this large investment that is only 1 year old.
Any input would be appreciated, as we would like to start swimming soon.


chem geek
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Postby chem geek » Fri 02 May, 2008 13:32

Starting with "normal" pool chemistry parameters of a pH of 7.5, TA of 100, CYA of 30, then one gallon of Muriatic Acid (31.45% strength hydrochloric acid) in 11,500 gallons of pool water would lower the pH to 6.4 while two gallons would lower it to 5.4, three gallons to 3.2 with all alkalinity wiped out. 16 gallons would have the pH at around 2 which is very low. Such low pH can damage equipment such as pump seals and can corrode metal such as copper in heat exchangers.

Lowering the pH to dissolve scale is not uncommon, but it sounds like the recommendation you were given was too extreme. Perhaps they meant to say 1.6 gallons of acid instead of 16 gallons.

You should test your water with your own good test kit such as the Taylor K-2006 you can get at a good online price here or the TF100 kit from tftestkits(dot)com here with the latter having 36% more volume of reagents so comparably priced "per test". You can also use The Pool Calculator to calculate the saturation index which was probably high to cause scaling. In the future, you can do things to prevent scaling such as reducing the TA level, keeping the pH lower, and reducing CH through dilution or using a water softener or sequestering agent.

Richard

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