Stay away from grapevine; Mikaila has a horror story of killing a tank of fish from fungus leeching out of grapevine. I had similar, thought mine was Mopani, might have been grapewood. They look near identical to me, light and dark blend.
Also, do not use any wood from the reptile section, just in case.
Petsmart has wood for fish tanks, some may be Mopani but they also have (at least here) Malaysian Driftwood. The nice thing about this is it is heavy so it sinks immediately (Mopani does not, it has to be weighted down until it is water logged which can take weeks for large pieces), has tannins but less than Mopani, and I've not yet heard of toxic fungus on MD.