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[piatotsini]

.

 

[OohFeeshy]

Not sure food dye would work TBH. Why not try something like coloured epoxy, or covering in a think coat of black sand?

 

[pica_nuttalli]

i've got a big chunk of texas holey rock and it's bone white. i doubt that you could dye it with anything fish safe, but i bet that it would look pretty sexy as-is on some black sand with solid red fish. maybe see about getting some nice dark plants to go with it, such as the red-brown type of crypt. or some of the darker anubius species.