I have one tubeless set up that is going flat over the course of a few days or so, its fine over a ride.

Do I just add some more fluid and re-seat?

what tyres are you using? Some can be very porous. You just need to shake the solution around more.

Put it in some water and see where the air is escaping from. It could be the bead, valve, a puncture or if it’s leaking around the nipples, there’s a problem with the rim strip/tape (If it’s not a UST rim).

Add some more sealant and do the tubeless dance ™ with the wheel out of the bike. Sometimes you can hear the air hissing out so you know where the wheel needs a good wiggle.

GB

Thanks – UST rims, 819’s

Tyres are Bonty XRs