Can I use softened water in my swimming pool?
The recommendations of the Pool Water Treatment Advisory Group in the UK are to maintain Calcium hardness between 75 and 150 ppm as CaCO3.
If you soften below 75ppm it will tend to slowly dissolve the (Calcium from the) grout on a tiled pool and also etch any Calcium based coping stones. Fully softening also makes it harder to maintain the pH as the water then has a lower buffering capacity.
So partially softening typical “hard” water is OK but fully softening is not a good idea.
In a typical hard water area of 300 ppm area most people do not bother to soften.
A block salt water softener can be used to soften the water but it would have to be done over a period of days as the softener needs to stop and make brine from the salt blocks which takes over one hour. Half fill the swimming pool and then soften the remainder to give you half and half and keep the level of hardness below about 150 ppm.
For a typical unit in an area of approximately 400 ppm run the softener at about 20 litres a minute for a period of 30 minutes and then stop for at least an hour. Start again and repeat as required.
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