We have had a Hot Tub for 30+ years. Read lots of articles, bought lots of chemicals. Now we have a simple formula for care.

Our water comes from a well, it's hard and contains iron. If your water is brown it may be iron or tannin's. An easy test for iron - 1/2 bucket of water add 1/4-1/2 cup bleach, leave overnight.
Bleach will oxidize the iron, leaving clearer water. You can also test with Iron Out, but do not use Iron Out in Hot Tub.

Only use liquid chemicals. Powdered chemicals will eventually make the water cloudy requiring you to drain and refill.

Almost all skin reactions are NOT caused by bleach, the culprit is PH.    PH, either high or low will burn your skin.

We use our Hot Tub almost daily 8-9 months of the year and have no tub related reactions. Controlling Ph is the key to a happy Hot Tub!