High Calcium Hardness

by John

High Calcium Hardness

by David Doig
(Hindly Pheonix Wigan)

I have just recently started a job to help maintain the swimming pool water. The swimming pool used to be run by the council and they were going to close it and knock it down. The local swimming club and volunteers have taken over the running of the pool and are really struggling with costs. I have my pool plant and water certificates and have done water maintenance for years.

The problem is the pool water hasn't been looked after for quite a long time so now the levels of Alkalinity and calcium hardness are all over. There is a 25m by 10m pool and a 12m by 5m pool. We have soft water and the alkalinity is around 20. I stopped testing the calcium hardness on the main pool when I used 15 tablets and the pool water was still pink.

I did the same on the small pool and didn't get a result either. I only know the way to drop calcium hardness by dilution. I drained some of the water from the small pool and added some more fresh water and tried the test again. I used 20 tablets which gave me the result of 780 which is way over what we should be.

We are using HTH calcium hypochlorite granular. I have used this before and acceptable levels can go up to a max of 500. The costs are a real problem for us at the moment just to stay open so we can't really afford to be dumping so much water to get the levels down. With the cost of chemicals, reheating the water etc.

I was wondering how would such high calcium hardness be affecting the water and if there was a way to keep the costs down to rectify the problem. Any advice would be much appreciated.
Thanx from a struggling volunteer pool that is trying to stay open for the local community.

Thanks for the question David

There's really no cost effective way to reduce the calcium hardness (CH) in a pool. You either need to do a partial or full drain and refill or have good pool water delivered. This is probably not what you wanted to hear. A high hardness, pretty much anything over 400ppm will either ruin or shorten the life of the heater. The coils will become calcified and stop working. The proper range for CH is 150 - 250ppm.

You must immediately stop using calcium hypo. This is adding calcium to the pool and causing you more harm than good. Use liquid chlorine. This will not raise the hardness like granular chlorine. You can also get scale formation on the pool surfaces, at the water levels, and scaling in the pipes, plumbing and filter. In some cases the water can become dull and cloudy. A work-around is to maintain a lower pH, 7.2 - 7.4.

Some people recommend using sodium carbonate which is pH Up or Arm & Hammer Super Washing Soda but you can't control where the scale will happen. It will cloud the water. Then you add a flocculant, allow it to settle, then vacuum to waste. You run the risk of scaling on the pool walls. This is why water replacement is safer and more effective. I wish I could be more help but a partial drain and refill is really the only way to go.

Hope this helps and have a great Summer.


Comment: Thanx for your feedback. I thought it was the only way to go but was worth a try asking. We are using a granidos system to feed the chlorine and acid together so we arnt set up to use liquid chlorine. Thanx again for your help.

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