blakej said:
Not a stupid question at all! Yes, the calcium hardness (CH) will measure the calcium in your spa. Based on the color of the test strip result, you will know the ppm range that you have.
One more thought I had for your spa was the use of Spa Perfect by Natural Chemistry (sku 04021). This is an enzyme that breaks down left over organic waste in the water - and will help you with the foaming and odors.
Test strips do not measure calcium hardness (CH). They only measure Total Hardness that includes both calcium and magnesium. You need a drop-based test kit, such as the TFTestkits TF-100 or the Taylor K-2006, to be able to measure CH. In fact, test strips are not good to use generally as they are not accurate for many of the measured parameters (see
this post). You don't want the CH to get too high in a spa or you will risk scaling, especially in the heater. A CH level of 120-150 ppm usually works reasonably well at preventing foaming. Note that if the pH is rising too much in a spa, that the Total Alkalinity (TA) should be lowered -- don't try and maintain 80 ppm if the pH tends to keep rising.
If one is only using a spa on the weekends, then chlorine or Nature2/MPS isn't usually a great choice because it requires more frequent dosing so if you aren't adding any chemicals during the week then the water can turn bad. The risk of that is lower with Nature2 due to the silver ions, but it is not zero. For infrequent spa users, using bromine with a bromine floater usually works better since it provides more consistent sanitation (see
Using Bromine in a Spa), BUT that isn't compatible with Nature2 (though is with Frog, but that isn't really needed if you are using Bromine). Also, if you have an ozonator in the spa, then bromine works better as well because ozone can reactivate bromide ion to bromine.
The least expensive approach is to use Dichlor to start out until you build up to around 30 ppm CYA and then switch over to using bleach (see
Using Chlorine in a Spa), but for that system one needs to dose every day or two so it's best suited to those who soak every day or two.
Enzyme products are not normally needed if one uses sufficient oxidizer to handle their bather load. Roughly speaking, every person-hour in a hot (104ºF) tub requires around 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach or 7 teaspoons of non-chlorine shock (43% MPS) to oxidize the bather waste. This assumes there is no ozonator. With an ozonator, these amounts will be lower, possibly half depending on the strength of the ozonator. The downside with an ozonator is that for spas not used frequently the ozone reacts with chlorine increasing the daily chlorine demand. As noted above, it ozone works well for bromine.
