Hello Robbie,
Try this ?
Buy a gallon or two of distilled water and begin to use it for misting the tank( as mentioned it will not stain the glass)
When the gallon container(s) are empty ---save them -----use them to refill from the tap and add your *aquatize.
The directions are on the container. *2 drops /liter ( exo-terra aquatize)
The small opening in the gallon container will keep him from getting into it
easy

Oh ! The distilled water will not hurt the frog if some gets on him when misting.
However, ( as Carlos mentioned ) It should not be used in the water dish for their soaking.

We should all be aware these water conditioners ...( ie Aquatize) are NOT a harmless chemicals.
Pets and children should be protected from them.
I would worry more about the cat drinking the aquatize
I would definitely protect the cat from this water in the future.
In fact, I would check the label for any specific instruction regarding this?

MSDS for aquatize
http://www.hagen.com/uk/msds/FS-A-PT...976-PT1977.pdf

Best, Lynn