Spa Water Chemistry – not so tough

Water chemistry can be a tricky thing. Tap water may be good enough to drink but that does not make it ideal for your hot tub. Compared to a pool there are also some major differences and challenges:

  • Extremely rapid bacteria reproduction at normal spa temperatures
  • Increases in pH, due to aeration, higher temperatures and speed flow through piping
  • Less active chlorine, thanks to the tendency for higher pH values
  • More organic-nitrogen compounds from bathers sweat, skin oils and flakes, which react with sanitizers to create chloramines
  • Less water available to dilute contaminants introduced by bathers
  • Increased calcium carbonate (CaCO3) scale due to higher temperatures and increased pH.

Hotter water means faster bacterial reproduction which means the importance of sanitizers is magnified. With less volume of water per bather means higher amounts of bather contamination for the sanitizer to deal with. * 1 person in a 1000 liter tub is equivalent to 40 swimmers in a small 40,000 liter pool

Bromine is a far more effective sanitizer compared to chlorine because bromine is still an effective sanitizer when pH levels rise,whereas chlorine becomes less effective as pH goes up. It’s very important to check pH levels and sanitizer levels frequently so as to keep in in proper ranges. Total Alkalinity is a sort of buffer to ensure pH bounces less. Typically Alkalinity wants to decrease which can cause the pH to rise and likelihood of scale to form especially on heater elements causing premature failure and costly repairs.

Calcium Hardness is also a concern. Water naturally craves calcium, if it’s not given the water will seek it out and it does this by leeching it from the polymers in the tubs acrylic shell which can cause cracking, blistering and fading. This is why often time if on city water there is a need to add calcium to the water gradually. Well water tends to be more calcium rich and may not require additional calcium. On that note however, there can be times when calcium is too high which can cause calcium deposits and even a sandpaper feel if it falls out of solution when pH levels drop or rise to dramatically.

It is always best to test your spa water frequently even using test strips so that minor corrections can be made without much difficulty or notice. However, sometimes it can be challenging to read these test strips or you may get strange color readings. In such cases bring in a water sample so that we can have a closer look and correct whatever is going on.


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