If youre going by the gauges/sensors on the rv they are totally worthless. I have 1 black, 2 gray, & 1 fresh water sensor & regardless of what's in them they either read 1/3 Or 2/3. DO NOT RELY ON ANY OF THEM & all the cleaners, ice cube tricks, magic elixirs DO NOT help. Sorry I can't help you figure how much water you have onboard, but if it's not leaking & you haven't used much then maybe it's still nearly full, but looking at the gauges won't help.
If still under warranty you could report they don't work, but in my opinion they'll keep your rv for 6-8 weeks then replace with the same sensors that after filled once won't be accurate either.