So I am looking to add some dither fish to my 150 gallon. I have tried using Giant Danios but they tend to get eaten and only swim at the surface. I am looking for something that will be able to survive with a clown knife, an aro, small pike and a malawi eye biter. I was thinking of going with a shoal of silver dollars. Is that a good fit and if so how many would you suggest I get?