I just picked up a complete used fish tank. The previous owners didn't seem to clean it very well so when I got it home I scrubbed it, then put the fish back into it with atleast 50% of the original water. I attached some pictures of the fish that came with the tank. Besides the opae which I just added I don't know what species any of the fish are. Also after the settling of the sediment I have noticed a white kind of dust covering everything in the tank. Also the larger fish seems like he may have fin rot. I included pictures. I would like to take care of this problem before it gets any worse. BTW its a 75g tank.