How-To Guides | ABCs of Spa Chemistry - Basics of Hot Tub Water Care

By keeping in mind the basic ABCs of spa water chemistry, you'll be assured a pleasant, healthy hot tubbing experience. If you are new to the wonderful world of hot tubs, start here!

Unlike bathtubs, we don’t drain hot tubs after use, so we must take measures to ensure clear, clean, sparkling water. This means balancing the chemical properties of our spa water so that it is neither too alkaline nor too acidic. It also means maintaining a sanitizing system to keep the water healthy and free of harmful microbes.

After reading this section, go to Preparation & Maintenance for complete directions.

Always maintain your sanitizer.

Warm water in spas would be ideal breeding grounds for harmful microbes if not for effective sanitizers to control them. Bacteria from our bodies, airborne mold spores, algae, and even viruses can find their way into the water.

Fortunately, we have great sanitizer systems such as Bromine, Nature2, and Frog.  These can effectively destroy microbes and keep the spa water safe and healthy.

Be Certain to Shock Treat

Shock treatment is the routine of applying a compound to your spa water.  The compound oxidizes or breaks-down the dead organic material left behind from your sanitizer system.

It also breaks-down non-filterable material such as dirt, soap films, hair spray and perspiration. Allowed to remain in the water, these contaminants provide a food source for bacteria and algae. Regular shock treatments eliminate them and the organics on which bacteria feed.

Regardless of which sanitizer system you use, periodic shocking is essential for clear, clean hot tub water. It will also allow your sanitizer to perform at peak efficiency.

We recommend using OxySpa non-chlorine MPS shock.

Dichlor granular chlorine is also a good shock to use at startup and to correct occasional water problems. (Dichlor should be pre-dissolved by itself in a plastic bucket of water, prior to adding to the spa water).

Note: If using Bromine as your sanitizer, the MPS compound in OxySpa also activates the bromide ion to become bromine. It then rapidly becomes the active sanitizer: hypobromous acid, in spa water. Upon reaction with contaminants, hypobromous acid converts to bromide, ready to reactivate with the next dose of Oxy Spa shock.

Control your water balance.

When the mineral components of spa water are correct proportion to one another, the result is balanced water. Balanced means that it is neither too alkaline (high pH) nor too acidic (low pH).

Balanced water has a more pleasant feel to the skin, and allows your sanitizer to work more effectively. We take periodic measurements of spa water with test strips to achieve balance.

Total Alkalinity (TA) & pH

TA is important. It is the measure of all the alkaline material in the water.  Really, it’s an indicator of the ability of the water to resist changes in pH - the water's buffering capacity.

TA that's too high is much less of a problem than too low. Always adjust TA first, then check your pH. Maintaining the proper TA will often bring the pH into line on its own.

Balance Water chemistry by adjusting its TA and pH with compounds such as Alkalinity & pH Up and Alkalinity & pH Down.


The hardness level of spa water - measured as the amount of dissolved calcium, is also important. Insufficient calcium hardness can sometimes promote equipment corrosion and also result in water foaming problems.

Although there's no practical way to reduce high hardness levels, it's easy to increase low levels by adding Calcium Hardness Booster.

Preventing Shell Stains

Prevent spa shell staining problems by adding Metal Stain Preventer when refilling your spa. 

Go to Preparation & Maintenance for complete directions.

OxySpa Non-Chlorine Shock

"It's about a 15 mile drive from our home to the nearest spa store. I thought I would give The Spa Depot a shot since you have free delivery. Wow!! Your Oxy Spa is half the price I was paying here for non-chlorine shock. Works excellent and I want you to know we will be back for our other supplies when we run low."

Ron & Julie Peterson
New Haven, CT

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