Hi, in the last few months I have started my first tropical aquarium and due to bad advice on what fish I could put in my tank I now have two tanks, tiger barbs in one and golden and rosy barbs in the other, I had 2 golden and 2 rosy, everything was going fine and then I noticed that one of the rosy barbs wasn't looking too well, it had lost weight scales missing and one eye missing! i couldn't believe it! so I watched... the other rosy is very aggressive and attacking it,( I didn't think the rosy barbs where aggressive) so I went to the aquarium shop for advice and came out with more golden barbs and 2 more rosy barbs (both male because they said that if I put females in the mix they are likely to be more aggressive)... they told me that there is less aggression when there is more of them because they do better in schools, I have put them in the tank and the aggressive rosy barb is bulling all the rosy's and they are all hiding in the corners, not sure what to do next except take the aggressive one out, but don't have anywhere to put it, also I have a 20 liter tank which now has 7 golden barbs and 4 rosy barb a total of 11 fish, which seems to me to be too many fish for that size tank but the lady at the shop said it would be fine. please any advice would be appreciated... thanks