(I rescued one fish and now everyone I know is giving me their pets). So, I will soon be the caretaker of two mice. I've read your care sheet. The cage they're in is 12x18" floor, by 24" high, and has three stories, but the top one is only a shelf 6x18". Does that count as 360" floor space? I'm also worried about their little feet and the wire shelf floors. Would that be safe or should I cover it with something solid. Also, are zip ties safe? I worry about hooks being sturdy enough and I don't
mind cutting and replacing them every day or two when I'll change out any fleece toys/bedding. They also don't have any toys, but I sew and can make a lot. Do you have any tutorials? (And as an afterthought, what would be the ideal water parameters on fire belly toads? The same for fish? I can't find any info anywhere)
Ah, glad you're taking in some mice! The cage is likely too small, but for now it will work. I strongly suggest making a bin cage, even though I dislike the way they look I love mine to pieces. But in the mean time I would cover the wire shelves with fleece, yes. Bare wire floors of any kind are dangerous and extremely difficult to keep clean.
Zip ties are perfectly safe! I've yet to see mice chew them significantly.
This post actually has a lot of good ideas for toys!
As for FB toads they tolerate a pretty wide pH level but it should be pretty close to neutral at all times. (7.0) and ammonia/nitrite/nitrates should be at 0 all the time. Waste levels will make them sick and especially hard or acidic water isn't good for them either. All amphibians I've read about can't tolerate especially low pH levels.