Those sandy's might need some rinses. They haven't ever been washed since TX hard water. That might not be helping. I did find that those sandys always had a stronger ammonia smell at night. I notice with any night diaper it's stronger, but the sandy's was worse.
Maybe you could soak the overnights in the toilet for a bit (I know, sounds gross) and then wring them out really well and put them in a separate pail in the bathroom. Just a thought.
I like this idea but Claire poops in the toilet so I never know when I might need it. I have been considering a sprayer. I wonder if I got a sprayer and just gave them a good spray down if it would help. Doing a separate bag in there would be difficult. The bathroom is just too small and there is no extra room. So glad this house is temporary.