Lynn is so right. If that frog swallows some gravel, he's in for trouble. I use smooth stones for both of my tanks, and they work great with Gnag and Bumpy.

I've heard of and seen "Turtle Cliff"s, however, I am inexperienced with them so I don't know how effective they are in cleaning up frog bio-waste.

Doing more frequent water changes when you first get the tank is a good idea, as the beneficial bacteria has not developed yet. Eventually, you can lessen the amount and frequency you change the water. However, do not let your guard down to ammonia. At least occasional water changes are a must, no matter the tank size, and occupants.

I'm not really sure how to clean your filter, either. If it were any other kind of filter, I could help you right away. As for the mesh, can you describe it a bit more?

Moss will almost always cause prolapse if ingested. I strongly suggest taking it out of the tank.

It's your choice whether to remake the tank. If you do, I suggest putting the frogs aside in a small spare tank with a good level of water, or a critter-keeper. Give their temporary home a hiding spot, or else they'll freak out. Nothing fancy, they'll only be in there for, at the most, a couple of hours.

Fred and Fat Frank love the names. I tend to go for quirky, peculiar, or strange names, as you can probably tell by Gnag the Nameless and Bumpy Digtoad.