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Swimming Pool Maintenance

Non-Chlorine Shock Treatment


This is simply using a non-chlorine based oxidiser to eliminate the chloramines. Potassium peroxymonosulphate is the most common; it's also known as potassium monopersulphate. Follow the instructions on the container. Note that it does not sanitise, it just oxidises chloramines. The similar sounding potassium persulphate is not suitable for pool shock treatment.

Other non-chlorine shock chemicals are:

  • Sodium persulphate: Can cause chemical buildup in indoor pools.
  • Sodium carbonate peroxyhydrate (sodium percarbonate).
  • Hydrogen peroxide: Just don't let the kids bleach their hair with it.


Advantages of Potassium Peroxymonosulphate

Disadvantages of Chlorine Shock

Swimming is possible after just half an hour. 6 hours before swimming - normally left overnight.
No undesireable by-products are left.

May leave by-products.

  • Calcium hypochlorite (a common chlorine shock) leaves calcium which affects hardness of water.
  • Cyanuric acid (from ordinary stabilised pool chlorine) affects acid level (which is what hurts the eyes).
Not affected by sunlight.

Cyanuric acid is added to pool chlorine to prevent it breaking down in sunlight. (See the Stabilising page.) Non-stabilised chlorine should be used for shocking to prevent cyanuric acid buildup, which means another chemical needs to be bought anyway.

Can be added before shocking is needed (ie, a pot at a time) since it is only used by oxidising chloramines, not killing bacteria.

Cannot pre-shock a pool with chlorine.

Chlorine levels do not need to be known before using, meaning less need for (expensive) test strips or tablets.

Combined chlorine levels ideally should be accurately measured to know how much extra chlorine to shock with. This is normally calculated by measuring free chlorine and total chlorine and finding the difference (a sometimes complicated process).

Uphill Battle

Sadly, at time of writing, not all pool shops sell potassium peroxymonosulphate. One I went into had actually never heard of the stuff, and when asked if they might consider stocking it in the future said "No, there isn't a market for it." They were wrong of course, for many reasons. A few of them:

  • It has many advantages over chlorine shock treatment (listed above) which save huge amounts of time treating the pool and in downtime in which the pool cannot be used. It also saves money on test strips.
  • It could be argued that test strips didn't have a market before customers actually knew they existed.
  • I was a customer looking for it, wanting to buy some. (Therefore there most definitely is a market for it, even if it's only a market of one person.)

Back to Chlorine Shock Treatment.

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