red tailed black shark

[tropic27]

The last time I was in the forum, I was worried because I didn't cycle my tank before adding new fish..Luckily w/ your advice..all my fish survived. Since the tank is cycled now & everything is going good, I went to buy some new additions. Originally, I had 5 silver dollars, 1 gray bichir, and one red tailed black shark. The shark never really came out of his hiding spot. When he did, he was peaceful & was pretty good friends w/ the Bichir. They would always curl up next to each other in the same cave. I was so happy that everything was going good, so I bought 3 small orange colored tetras..Not sure what they really are, but they resemble feeder goldfish w/ some black blottchy line on the side..(hey, they were only $1.50) & I also bought 1 Albino Buenos Aires Tetra, which was the last one they had & they weren't going to re-order it, so I got it cheap. Well, I thought that since these were small, peaceful fish..everything would be ok. The silver dollars & the Bichir don't mind the addition..but my shark is freaking out. Not only is he chasing the tetras like crazy, but he is even being aggresive towards the Bichir & silver dollars. The Bichir trys to curl up to him like always, & the shark starts to snip at him & nudge, or head butt him out of the way!! Also the shark changed color..he is no longer black..he turned a light grey color..Is this a sign of stress, or the wrong diet?? Also..will he get used to the newbies or will I have casualties? ( I have a 50 Gal tank)