i've kept 11 rbp. when i first got them i didnt use it, until my first wate change. i didnt see any thing different when i poured in tetra blkwater extract. yeah they are from the amazon. arowana are from the amazon aswell, u dont really need it. like the other guys said u can use malaysian driftwood, it does the same job. but blackwater works wonder if ur tryin to breed, it promote fish activity... kinda like a "high" for them. if u need more assistance check out piranha-fury.com , its a great site dedicated to ps. dzb912 is right it makes it cloudy as hell. so if ur going for the amazon isotope go for it. if u want a clear tank dont put alot it. maybe 2-3 cap full. good luck bro.