How to keep a 500 gallon hot tub clean

Our hot tub is a 500 gallon commercial hot tub that we leave at operating temperature (100' fahrenheit) 24/7. Here's the cleaning procedure that seems to work for us.

Test the chlorine and pH levels of your pool. When you first start out, I recommend testing daily. Eventually, you'll get a feel for the rhythm of your tub and may be able to reduce testing frequency. In my experience, test strips are pretty useless. Use this chlorine kit instead (or something like it):

http://www.homedepot.com/p/5-Way-Pool-and-Spa-Test-Kit-62364/203796265

For our level of use, 1/3rd cup of chlorine and 1/3rd cup of HCL every couple of days is sufficient. If your tub is used more frequently, you may need to increase the testing frequency.

We use Home Depot's house brand of liquid pool chlorine:

http://www.homedepot.com/p/HDX-1-Gal-Pool-Care-Chlorinating-Liquid-2-Pack-20128HDX/206809041

...and the Home Depot brand of hydrochloric acid:

http://www.homedepot.com/p/HDX-1-Gal-Muriatic-Acid-2-Pack-10031HDX/206809317

Since our hot tub is used almost exclusively at night, I don't bother with stabilizers like cyanuric acid, which slow UV degradation. If you use the tub during the day time, you may want to use such a stabilizer or you may need to add chlorine more frequently.

Our spa is also set to filter the water 1.5 hours every day. Here's the filter we use:

https://www.amazon.com/gp/product/B0028668WS/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1

Filter gets changed out once a year. Once a month or whenever the water gets foamy, I drain and replace the water altogether. I also rinse off the filter and clean out any sand or other debris that's fallen into the tub.

Troubleshooting:

Problem: Water is cloudy and/or smells.

Cause: Bacteria or fungal growth.
Solution: Add more chlorine or replace the water.

Problem: Your skin itches after you get out of the tub.

Cause #1: Microorganisms in the water are irritating bathers skin. Pseudomonas bacteria are a common cause of "hot tub folliculitis."
Solution #1: Add more chlorine.
Solution #2: "Shock" the system with a higher than normal amount of chlorine (5x or more)
Solution #3: Drain and replace the water.

Cause #2: Too much chlorine.
Solution #1: Test the water's chlorine levels. If too high, drain and/or add more water.
Solution #2: Switch to a non-chlorine based cleaning system.

Problem: Water is foamy.

Cause: Dissolved oil and soap from skin, shampoo, and other other hair products.
Solution #1: Anti-foaming agent. Temporarily knocks down the foam, but you have to re-add or the foam will return.
Solution #2: Drain and replace water.

Problem: Sand or grit on the tub floor.

Cause #1: Chlorine tablets.
Solution #1: Stop using chlorine tablets.

Cause #2: Sand or grit from bather's feet.
Solution #1: Ask bather's to wash/wipe their feet before entering tub.
Solution #2: Vacuum up grit with a pool vacuum.