What is the deal with drop in salt water chlorinators for hot tubs?

[lounge_lizard]

You plug these units into a Ground protected receptacle , add salt and they generate chlorine. Pros Cons?
I have a salt water pool but currently run two step bromine for the spa. They seem to run $200 to $250 in Canada.

 

[JasonLion]

SWG systems can be used in spas, but they aren't nearly as good a fit as they are for pools. Chlorine demand in a spa very much depends on how often you use the spa, and can vary rather dramatically when you vary in how much the spa is used. SWGs are good at producing constant amounts of chlorine and much more of a pain when the chlorine demand is varying all over the place.

One compromise some people use is to use the SWG to meet the fairly low constant chlorine demand, and then manually add more chlorine manually right after each use to meet the variable part of the demand.

 

[chem geek]

Jason summed it up nicely. The SWG for spas makes most sense for those who don't soak every day or two since it's a way of maintaining a background level of chlorine in the spa. This is especially necessary when one has an ozonator since ozone depletes chlorine. When one does soak in the spa then one would usually need to add additional chlorine after their soak to handle the bather waste. If you have an ozonator and if you don't soak for very long, say one person for 15 minutes, then you can probably get away with just having the ozonator and SWG take care of things. The only way to know for sure is to test the chlorine level, say, 4 hours after the soak to make sure you still measure at least a small residual of chlorine (i.e. not < 0.5 ppm FC) and measure again around 24 hours after the soak to see if the level is back to the expected amount (usually 1-2 ppm FC if that's where you like to start your soak).

Also note that some spas do not use high quality stainless steel so are more subject to metal corrosion from higher salt levels. It may also void the warranty for spas still under warranty.