I had 5 zebra danios they where fine in the tank could always see at least 3 of them at all times I got them to put ammonia in my tank so It would cycle I have now cycled my tank so was going to give them away but have grown fond to them and am keeping them but I put a small silver shark in today and an orange spotted pleco and the danios disappeared and I was searching my tank and found 3 behind the filter just staying there and they where really active before I put new fish in and I'm not even sure if there is 5 I can only see 3 of them now am just confused why they just won't move at all they just sit next to he filter just bobbing around.