When you add chlorine after a soak, some of it will be almost immediately consumed by the bather waste from your soak if your FC got to near zero during the soak. If you want to test the calculations, then you'll want to do so when adding chlorine when there is no bather load, such as testing in between soaks or just before your next soak. Since you soak every other day, I suggest you do a test during the day at least 24 hours after your soak and be sure to do the test when there is still some measurable FC, such as 1 ppm. Wait about 10 minutes or so with the circulation pump running before measuring again after adding the bleach -- do not wait more than 1 hour before measuring since the ozonator will react with the chlorine reducing its amount.
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Amore Bay says it's a 415 gallon tub so 2 people soaking for 30 minutes would need 5 fluid ounces of 6% bleach to oxidize bather waste which in 415 gallons would be 5.8 ppm FC. However, with your ozonator, you may not need to use as much bleach since it should be able to oxidize some of the bather waste. On the other hand, when you are not using the tub the ozonator will be reacting with chlorine so ozonators are of benefit when a tub is used a lot, but not when used infrequently. In your case, it's probably of some benefit.
As for the calcium hardness indicator dye, Taylor calls it a deep blue, but I agree with you that it looks more like a deep purple. The reagent is not compromised with that color. I don't what color it changes to if/when it goes bad.