How to Maintain your Hot Tub with Chlorine

Chlorine is the traditional pool and spa sanitizer, but unfortunately it is also the nastiest and one of the the hardest sanitizers to use correctly. Chlorine is very sensitive to pH fluctuations and doesn't work effectively if the pH is outside of the optimum range. In addition, chlorine can be smelly and can cause skin irritation if used at any more than a very low concentration.

In order to use chlorine to sanitize you spa you'll need to perform the following steps:

At Each 3 Monthly Water Change

Clean the Plumbing:
Add half a bottle of Spa Flush or an alternative plumbing cleaner to your existing tub water and turn on all jets and pumps for at least 30 minutes. Remove the filter(s) during this process if you are able to run your pumps without the filters in place. It’s preferable to leave the plumbing cleaner to work overnight if possible.
Drain the Tub:
Use a non-scouring pad to wipe away any deposits left on the shell as the water drains. For significantly dirty spas use a specialist spa surface cleaner. DO NOT use any household cleaners.
Clean the Filter(s):
Rinse any debris from between the pleats under a running tap, or use a Water Wand on your garden hose. Place the filter(s) upright on the bottom shelf of your (clean) dishwasher and use a powdered filter cleaner in the powder dispenser and run the dishwasher on a normal 50ºC wash cycle. If your filter(s) won’t fit in the dishwasher then soak them overnight in a suitable container using a powdered filter cleaner, then rinse thoroughly.
Allow your filter(s) to dry naturally before replacing them in the tub. This is important because the filter material will last much longer if it is allowed to thoroughly dry between uses. Filters can take a very long time to dry so it’s a good idea to keep a spare set and to rotate them each time you clean them.
Refill the tub with clean water.
Balance the Water:
Test the water using chlorine test strips and adjust the Total Alkalinity and pH , using the directions on the water balance product containers:
  • the Total Alkalinity should be within the range: 80 - 120 ppm
  • the pH should be within the range: 7.2 – 7.8
  • the Total Hardness should be in the range: 250 - 500 ppm
You should first adjust the Total Alkalinity, then when that is in the correct range adjust the pH and finally the Total Hardness. You must persevere until you get the correct balance because the chlorine won't work effectively if the balance is outside the required range.
Add the Chlorine:
You will need to use chlorine granules to give an initial shock does of chlorine to a freshly filled spa. Pre-dissolve the weight of granules recommended on the product container in water in a clean plastic bucket, stirring well to make sure that the granules are completely dissolved. Apply the solution to the spa whilst the pumps are turned on to aid distribution. You should aim to maintain a chlorine level of 50ppm for 1 hour or 20ppm for 2 hours, you may need to add additional chlorine to maintain this level.
After the initial shock, allow the chlorine level to reduce to 3-5ppm. Test the water after 30 minutes and at intervals, if necessary, and do not get into the water until the level has reduced to less than 5ppm.

Regular Maintenance

Check the water balance using chlorine test strips and adjust as necessary to maintain the range specified above.
Apply a maintenance dose of chlorine by pre-dissolving granules in a clean plastic container and applying to the spa with the pumps running to maintain a reading of 3-5ppm.
As an alternative to applying chlorine granules daily you could use 20g Chlorine tablets either in your spa's in-built chemical dispenser or in a floating dispenser. Chlorine tablets dissolve slowly and evenly to give consistent and long lasting chlorination, avoiding the need for daily dosing, but some tablets have a very low pH and so they can consequently reduce the pH of your spa water leading to the potential for equipment damage and skin and eye irritation. Do not place chlorine tablets directly into a skimmer basket or elsewhere in your tub.
NB. If you use chlorine tablets you will still need to check and, if necessary, adjust the water balance daily.
Use a chlorine-based shock treatment to remove non-filterable organic contaminates. You should shock your tub weekly as a matter of course. It is also a good idea to shock after any period of very heavy use or if children have been in the tub (let’s be honest, it’s not a very attractive proposition to get out of that lovely hot water to find the loo!).
NB. Don’t check the chlorine level for at least 12 hours after you have applied the shock because you will get an incorrect reading.
Clean your filters weekly as described above.
Clean the plumbing and change the water as described above.

Chlorine Facts

Here are some things that you should know if you decide to use chlorine as a sanitizer:

  • When chlorine reacts with organic material in the water it forms chloramines. Chloramines are a bi-product of the chlorine working to kill bacteria, they do not perform any sanitizing themselves, but it is the chloramines that give that 'chlorine smell' to a spa and sting your eyes.
  • chlorine only works properly ie it only kills bacteria when the pH of the spa water is correctly adjusted. The pH of the water changes as the chlorine level changes, so maintaining the correct water balance can quickly become a difficult juggling act!
  • chlorine is a potent bleach and is highly carcinogenic. According to the U.S. Council Of Environmental Quality: Cancer risk among people drinking chlorinated water is 93% higher than among those whose water does not contain chlorine.