[MollyAttack]

I wouldn't do any geckos, they are not swimmers. They will probably drown if they get too far into the water, and even if they stayed out of the water, they wouldn't be utilizing the whole tank so it's sort of a wasted space.

Mossy Tree Frogs are so cool looking! I think you should do those. Fire-bellied Toads would also do the job. Maybe a species of newt or salamander would work? You should check out Caudata Culture Forum. They have a TON of info on newts and salamanders. Here are the care sheets they have on their website too (you have to go up near the top to the species tab and click "Caresheets") Caudata Culture Species Care Sheets.

 

[MollyAttack]

Okay, so I don't know much about this species and I could be totally off on this (someone please correct me if I'm wrong) but Amazonian Milk Frogs might like it in there. I'm not sure if they're diurnal or not.

And geckos are definitely out now if you're looking for something active during the day, haha.

Edit: Nevermind, Milk Frogs are nocturnal. Not sure they would do that well in a palu anyways cause they're mostly arboreal.

 

[MollyAttack]

Marbled newts might be more difficult to take care of than mossy frogs. Marbled newts' diet might be a bit pricey and you'd have to induce a temperature drop somehow during the winter months. They're also very sensitive to water quality (all newts are). They might be tricky to find from breeders, not sure how many of them are being captive bred (wild caught ones will surely die). Is the palu already set up? You'd have to replace a glass lid with a screen lid for marbled newts for ventilation.