Hey, Paz!
The Tetra whisper can work in less than 5 inches of water, I currently use it in my fire bellied toad setup. They have a back clip you can take off and use the suction cups. A pack of about 12 Refill filters will cost you about 8 bucks. I found both of these at my local petco.
If it helps, I use tapwater for my FBTs and had fish for a while before I had to get rid of the fish due to the large bio load causing the water to turn brown. I suggest getting a tetra safe water dechlorinater, I've been told by members on here that tap water has more nutrients that bottled or store bought water has, just make sure you dechlorinate first! I wouldn't worry to much about Dechlorinating your water you put in while doing your weekly 15-10% water changes since the water in the tank will mix, I do it just to be safe. I did not have a single problem with the fish until I took them out.
I would hold off on the frogs until you get an acclimated tank.
Alternatively here is page that goes more indepth on the care of these guys more than I ever could. Since i'm more educated on fire bellied toads.
http://aquaticfrogs.tripod.com/id13.html
Keep in mind that the big pet chains who list guides on how to care for their animals will mostly be wrong.
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