I can kind of picture what you're descibing, I've definitely had similar ideas but never tried any. It's a cool setup, although snakes terrify me. I was moving a wood pile earlier this summer and there were so many garters in it. Every like 10th log I'd pick up there'd be one and every time it would make me jump.
I really like all the stones in the tank, looks really zen. Maybe for the next version you could create a more solid transition with big rocks or a custom 3d background sort of thing. That way you have a more defined/safe tank space, while still being able to keep a garter friendly area out of the water. Then replace that sponge filter with a fountain pump with a sponge prefilter and have that feed into a tube that creates the waterfall.
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