I got a citron goby two days ago and noticed it has some black looking dots on his tailfin. Should I be worried or is there anything I need to do? I have in him a QT right now with a Royal Gramma that I got the same day. It has been eating the Mysis and brine shrimp I've fed to it. The second picture it's harder to tell but the first pic shows them on his tailfiin.