Hello,
leaving the spa uncovered in direct sunlight will use the bromine up very quickly and can cause acrylic damage to the spa, the spa cover should be in place whenever the spa is not in use.
I would suggest having the floating dispenser open enough to show 2 full pucks to start and wait 24 hours, retest the water chemistry, and adjust it until you see a reading between 5-10ppm, levels higher than that are not necessary. High sanitizer levels and heavy shocking is hard on pump seals and other components in the spa and can cause them to prematurely wear and fail earlier than expected. When shocking the spa use a non Bromine/Chlorine shock(Arctic Pure Refresh) as using a bleach will increase the sanitizer level in the spa when it is not required and shocking the spa should be done once a week and the cover left open for 20 min while it is burning off the bacteria.
Regards,