African Clawed Frog Tank adjectives set up, but I own a request for information almost filter/breathing room?

I originally had an inch or so of air between the water top and reading light in my 20gl tank, but I filled it up to a few centimeters between contained by order to make the "waterfall" from the filter disappear straight into the tank so as to not disturb the frogs. I be wondering if this was ok or not for them because I know they have to come to the top to breathe. Any help out is appreciated.
Answers:    They can breath in like 1mm cuz all they have need of to do is stick there little nose things up and breath. just don't spread it up too far clawed frogs are know to jump out of tanks thew he filter hole
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