Possibly the biggest learning curve for new hot tub owners is water chemistry. In this article, we'll break down the essentials in under 10 minutes; by the end, you'll understand what your spa needs and why. These also apply to all-season pools.
This article aims to help you understand water care but doesn't go into a specific care routine - for that, you can check out our free downloadable water care card.
Why do we need to add chemicals to the water?
Unlike a bathtub, hot tubs and other spas stay filled all the time. Without treatment, this water would develop bacteria and algae rather quickly.
The Big 4
There are 4 essential chemicals/measurements for spa water.
1. Sanitizer
The most important chemical, sanitizer is used to kill bacteria. If your sanitizer falls too low your water will develop bacteria and algae, and if it gets too high it can irritate your skin and damage your hot tub.
When it comes to sanitizing your hot tub, there are two options deemed safe by Health Canada: chlorine and bromine.
Chlorine
Pros:
Less expensive
More effective outdoors
Widely available
Cons:
Shorter lasting
Harder on skin*
More likely to smell*
Note: these last 2 points are common misconceptions. Skin irritation is usually due to low pH (more below). The chlorine smell most of us are familiar with is usually due to low chlorine and organic contaminants: body oils, cosmetics, etc. (more below).
Bromine
Pros:
Longer lasting
Less likely to smell*
Cons:
More expensive
Less effective outdoors
Harder to wash off skin
We recommend chlorine because it's less expensive and better suited for outdoors due to it's UV resistance. Bromine can be a good alternative if you have concerns with chlorine sensitivity, but keep the above misconceptions in mind.
Although chlorine and bromine serve the same purpose, they should not be used interchangeably. If you'd like to switch from one to the other, you must complete a drain and fill.
2. Shock (Oxidizer)
Sanitizers are great at killing bacteria but struggle to break down organic contaminants like body oils, cosmetics, etc.
Oxidizer, most often referred to as "shock," breaks down these contaminants. As previously noted, it's actually sanitizer (particularly chlorine) interaction with these organic contaminants that causes the "chlorine smell." Shock helps prevent this.
Shock isn't measured on test strips; it just serves as an aid for sanitizer.
pH measures the acidity of water. If your pH levels are low, your water is acidic, which causes skin and eye irritation and corrosion. If your pH levels are high, your water is basic which can lead to scale formation and reduced sanitizer effectiveness.
You adjust your hot tubs's pH using a pH increaser or pH decreaser.
Alkalinity measures pH stability - the water's ability to resist changes in pH. If it's too low, pH won't stay balanced; if too high, it becomes difficult to adjust.
You adjust your hot tubs alkalinity using an alkalinity increaser or a pH decreaser ("alkalinity decreaser" doesn't exist, but it would be the same thing chemically).
These don't need to be monitored as closely as sanitizer, pH and alkalinity, but they're important to keep in mind.
Stabilizer (chlorine only)
If you're using chlorine your test strips will also have a measurement for stabilizer (chemical name cyanuric acid) - this is added to chlorine to protect it from the sun's UV rays.
As you add chlorine over time, your stabilizer will increase; once it gets too high, chlorine becomes ineffective. The only way to fix this is to replace the water - one of the reasons a drain and fill 3-4 times a year is important.
Calcium Hardness
If you fill your spa with water that's too soft, it can lead to corrosion; if it's too hard, it can lead to scale buildup. Both can damage to your hot tub.
You can increase the hardness of your water with a calcium increaser, but the only way to decrease the hardness is by diluting with freshwater.
Most people using hard water use a stain & scale control product that prevents calcium and mineral scale buildup in the hot tub.
The 2 most essential measurements for your spa are its sanitizer level and pH. Shock helps improve sanitizer effectiveness and smell (but isn't measured), and alkalinity shows how stable the pH is.
The goal of this article is to emphasize the essentials listed above, but if you're interested in a more complete chemical list, continue reading a bit further.
Other Popular Chemicals
Filter Cleaner
Giving your filter a regular clean is important to extending its life and preserving clean water - a filter cleaner does just that.
When organic contaminants and detergents (usually from bathing suits) are introduced into the water, it often leads to foam. A quick shower before you enter can help reduce this, but if you're still having issues, there are a couple of options.
The most popular solution is a special sponge that absorbs the contaminants - Zorbie is the most popular.
