Now that we are in the slow season for swimming pools, we would suggest that pool owners do a chlorine shock treatment in their pool.

Time to Shock your Pool — Pool Maintenance Experts in Alstoneville, NSW
Though the disinfection level of pools are maintained during the year, there are some bacteria that need to be shocked to be removed from the water, ie. E.coli, Cryptosporidium, shingella.

Shocking a pool involves raising the chlorine level to over 10 parts per million (normal level is 2-3ppm) and keeping it there for 2 days. It will then take a couple more days for the level to drop back down. To be safe, we would recommend the pool not be used for at least 5 days during this time.

The easiest way is to use liquid chlorine – 4 times the dose on the bottle. Make sure the pool cover is not used during this time as a high chlorine level will damage the cover.