80% humidity?

So I live in the UK & it's pretty humid here, usually around 60% in my home
Im using a tub set up with ventilation holes soldered in, with paper towels as substrate & a large expo terra water bowl
The substrate/towels are never wet & the tub never condenses up on the inside, my digital thermo-hygrometer reads at 80% (It's Lucky Reptile one), the tub is dual lidded so I've been opening it for a little bit to bring the humidity back down to around 60% - 70%, supervised of course & it gets shut when I'm not around
I went to change his water bowl yesterday to find it felt a little slimy inside/where the water had been, so a I gave it a good scrub with soap, water & scouring sponge, gave it a good rinse & refilled it with fresh water
I just don't want him to get an RI from the humidity being too high & I just wanna know what TOO high is
Had him around a month & he hasn't shed with me yet so obvi I can't comment on any issues with that yet

I'm just notorious for whittling (Worrying for you none UK folk) about every little thing n I wanna do right by my bab

As long as you have enough airflow, 80% is fine. How many holes do you have and what size tub? How much water is in your bowl? What kind of heat source do you use?

50l Staples tub 675 x 445 x 230 mm with 24 holes down both lengths of the tub & an UTH controlled by a herpstat thermostat & the bowls around 1/2 - 2/3 full & placed on the cool side
It never smells damp when I open the tub if that makes sense, unless he's peed or pooped in which case it smells funky anyway

You have good airflow, so that's fine.
Also, your water only has to be around the height of the snake