You need a test kit
Nor sure how pee gravel is packed, but you need enough for 64 cubic feet.
You need 13 yrd's of fill
About 6,042 gallons of water.
Chlorine has 17 protons.
6
Chlorine is a meta element. Atomic mass of it is 35.
16 sq ft*0.5 ft = 8 cubic feet.
The best thing to do if you are inexperienced in pool maintenance it to take a sample of water from your pool in a clean bottle from about an arms length in depth to you local pool shop. There they will test the water for free and tel you how much chlorine your pool needs. Take along the dimensions of the pool as well for them to calculate the requirements.
Although chlorine is a poisonous gas which can kill people, and chlorine was used for that purpose in WW I, it is virtually impossible that your hot tub will contain so much chlorine as to endanger your health. It's safe.
There is no direct conversion between liquid chlorine and chlorine tablets because they come in different forms and concentrations. It's best to follow the manufacturer's instructions on how much liquid chlorine is needed to achieve the same sanitation level as a 3-inch chlorine tablet in your specific pool or spa.
If you have added too much chlorine to your pool, you can dilute it by adding more water to the pool. You can also let the chlorine levels decrease naturally over time with exposure to sunlight. Alternatively, you can also use a chlorine neutralizer product to help reduce the chlorine levels quickly.
If you have too much combined chlorine in your pool, it can lead to eye and skin irritation, as well as create an unpleasant smell. To reduce combined chlorine levels, you can shock your pool with a chlorine shock treatment, which will break down the combined chlorine compounds and free up the chlorine to sanitize the water effectively. Regularly maintaining proper chlorine levels and practicing good pool hygiene can help prevent the buildup of combined chlorine.