does the 3 inches include the tail? if so, a 5 gallon will be fine for awhile. when they double in size, you can move them up to a 10g.
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4.1 snakes, 4.6.1 crested geckos, 0.1 gargoyle gecko, 0.0.2 red-eyed tree frogs, 2.0 devon rex cats, 1.0 betta, 0.1 sun conure, 1.0 lovebird