Sometimes a beer trap with work for slugs, but you have to cover it so your frogs don't get into it. The hand-picking method (flashlight at night) as someone mention, works, but you have to keep on it. How deep is your waterway? (One of mine is a paludarium with an aquarium section with tropical fish.) If it's deep enough for aquarium fish, clown loaches will clean up snails. Otherwise, removing the water plants, washing them and removing any snails you find may control them a bit, but still doesn't get rid of them. Other than removing your frogs to a critter keeper for the duration, trying one the the snail-begone products, then changing the water several times, (and that might not even work,) I've never discovered a safe way to get rid of them in a shallow waterway.
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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