Overchlorination - How to deal with it and get the pool open for business again!

Posted by poolplantcourses.com on Friday, July 22, 2016 Under: Pool Water Chemistry

It may be necessary to decrease the levels of chlorine on occasion and certainly following superchlorination. If you are going to be dumping a significant quality of swimming pool water for any reason, there would usually be a requirement to let the local water authority know and they would almost certainly require you to eliminate all traces of chlorine from the water before they granted permission to discharge (chlorine is harmful to aquatic organisms).

In normal operations, it would usually be better to bring the chlorine levels down by simply diluting the swimming pool with fresh water. This is safer and would contribute to less chemical pollution as well.

If you do need to decrease the chlorine quickly though, the chemical to use is sodium thiosulphate. The principle to bear in mind is that it takes 5g of sodium thiosulphate to neutralise 1g of chlorine. So if, for example, you had 10.00mg/l of chlorine in a 300m3 pool, that equates to 3000g of chlorine in the pool, since each m3 would have 10g of chlorine in it, and 300m3 X 10g = 3000g. The simplest thing to do would be to calculate how much sodium thiosulphate you would need in order to decrease the free chlorine level by 1.00mg/l. See he worked example below:

300g chlorine X 5g sodium thiosulphate = 1500g

So, in this particular example of a 300m3 pool, it would take 1500g of sodium thiosulphate to reduce the free chlorine level by 1.00mg/l/

From here, the same steps can be taken as given above in order to create a jug for the purposes of hand-dosing sodium thiosulphate (different jug – NEVER mix chemicals). Then, just add the required number of jugs in the same way as for adding calcium hypochlorite. So, in the example given, we would be adding 8 jugs of sodium thiosulphate in order to get the free chlorine down from 10.00mg/l to 2.00mg/l.

In : Pool Water Chemistry 

Tags: "decreasing chlorine"