So correct me if im wrong but isnt live rock a biological filter?
You're not wrong, LR
is a biological filter - but, it is a biological filter because of the live *bacteria*. Again, an antibiotic is not specific in what bacteria it kills.
I don't understand how they can market it as being "safe" for biological filters, when biological filters are based on beneficial bacteria.
i wanted to put it in the quarantine tank with the fish because this fish needs the live rock to live (green madarine goby)
The Mandarin is going to need a lot more than this rock to survive. I'm pretty sure I posted in the other thread where you were asking about this. In any case, this single 8lb piece of LR
is pretty much irrelevant to the Mandarin's survival - so don't take the chance and put the LR
in the Q tank.