Spa Sanitation in a Nutshell

There are essentially 5 ways (regimens) to sanitize your spa water. Here are some relevant facts. “Best” are highlighted in yellow:

Regimen	Dichlor	Brom Tabs	Salt	Metallic Ions	Biguanide¹
Primary Sanitizer²	Chlorine	Bromine	Either chlorine or bromine	Generally silver (Ag)³	Polyhexamethylene biguanide (PHMB)
Water Changes	Requires changing spa water at least 4x annually	Change spa water 3x annually	Annual water changes	Change spa water 3x annually	Change spa water 3 – 4x annually
Advantages	Low Cost	Low Cost	Low long-term cost Lowest chemical use Beneficial for those with skin issues	Lower level of chlorine or bromine needed	Halogen free⁴
Disadvantages	pH must be maintained in the 7.2 – 7.6 range. Must be added to spa water twice a week	Brom Tabs must be replaced every 10 days or so.	High initial cost⁵	High operational cost Chlorine cartridges often must be replaced more often than the advertised “monthly”.	High operational cost Incompatible with all other sanitizing chemicals including MPS⁶ and ozone Requires extreme precision Often have issues with pink slime & white-water mold Can damage plastic⁷
Skin Sensitivity	Some people are very sensitive to chlorine	Gentler than chlorine	Best for those with sensitive skin	Gentler than straight chlorine	Best for those with sensitive skin
CYA?⁸	Approx. 50% CYA	Bromine formulations include some dichlor	None	None	None
Oxidizer	MPS	MPS	MPS	MPS	Hydrogen peroxide
Maintenance	All spa sanitation regimens REQUIRE weekly testing and adjustment, at a minimum. Anyone saying differently is not being truthful.

Footnotes:

Biguanide has traditionally been used in a hospital setting as a sanitizer. Around 15 years ago it became available as a spa sanitizer.
The “chlorine” and “bromine” in spas are actually rather weak acids called hypochlorous acid or hypobromous acid. Chlorine and bromine are just shorthand names for these.
Silver is known to have mild antimicrobial properties but has insufficient efficacy to be approved by the EPA as a stand-alone sanitizer. It is always used in combination with either chlorine or bromine.
Chlorine and bromine are halogens. For the chemistry buffs, halogens are those elements in the 2nd column from the right in the Periodic Table of Elements.
The Salt System equipment make the initial cost high however, the lifetime cost (5 – 10 years) can be quite low.
Potassium peroxymonosulfate, also known as “Chlorine-Free Shock.”
Many spa manufacturers disavow the use of biguanide in their spas in their warranties.
Cyanuric acid (CYA) is a chlorine stabilizer used in dichlor. However, it also reduces the bacteria killing efficacy of chlorine and continually builds up in the spa with each application. This is the primary reason a dichlor sanitized spa requires a minimum of 4 water changes annually.