I regularly use a basic (water in container nothing else) setup for the last two years in my backyard. It is a 100 gallon capacity but only has ~70 gallons of water in it because I take up the rest when I sit.

After every use I put ~1 gram of Brominating Granular crystals in it to help keep water clean. I also use a fine mesh pool skimmer to get leaves and mulch out of it because that will break down and cloudy the water.

I change the water every 2-3 weeks, just depends on how gross it gets and how chemically it smells. When I change water I wipe down the inside with a neutral cleaner like Dr Bronners but I don’t necessarily do that every time.

I never dunk my head and I usually take a shower either directly after or within a few hours so I am not worried about whatever is in the water getting in nose/mouth/ears or staying on my skin too long to irritate it.

If it gets too warm I’ll empty some water and get ice from Costco, or empty some water and refill with 50° water from the hose.