Oh, that's right.. Tank toppers don't come for 40 gal tanks, lol. I've not trued tank topper, but they loom fun, with some moderations
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Emsy, Hams enjoy climbing, and like you, I'm concerned with high falls. Can you lower the hammock? Gizmo hanging off the mesh lid, I'd say, is not a safe thing for him to be doing, nor do you want him to form an habit of doing it. It's like monkey barring in a sense.