Hello, I've been trying to find black sand for kuhlI loaches. I 've been looking at and researching a lot of brands, but some are really expensive, others, upon reading reviews, are not sand, but died pieces of metal and plastic (?!). I could not imagine it would be this hard! Loaches are said to really like to dig and play in the sand, so I imagine it has to have no really sharp particles and be durable (people say dye comes off some substrates). Any recommendations for black sand?