I use a 3-4 inch layer of coarse rock and gravel mixed with hunks of charcoal for the bottom. This has a layer of the black plastic weed-inhibitor cloth used for gardens to keep the substrate from sifting into the drainage. (It has tiny holes in it). Then I siphon off excess water from one corner with an aquarium airhose that dumps into a container. I use this to water my house plants. The airhose is siliconed in place on the inside corner, and I have a 30cc syringe (not leuer-lock, but plain tip) to start the siphoning whenever I notice any extra accummulation of water. It's low tech, easy to set up and works. Fungi really aren't a problem in dart tanks. They are not pathogenic to the frogs. Different kinds will come and go, but can be ignored or simply wiped off the glass. It's just a part of the overall balance that makes dart frog tanks a lot easier to maintain than others.
I think 10 gallons is just a bit small, but that depends upon what you want to keep. My smallest tank is 20 gallons and has four blue auratus. I have two tall 30 gallon hexagonal tanks for my thumbnails, a 72 gallon bow front with a waterfall, stream and shallow pond for the leukamelas and a 135 gallon paludarium (half land, half aquarium) with waterfalls, for the galactonotus. The same drainage works for all of them.
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Patty
Lost River, Idaho
4 D. auratus blue
3 D. galactonotus pumpkin orange splash back
5 D. imitator
4 D. leukomelas
4 D. pumilio Bastimentos