Because I wanted to focus on shrimp. The fish would eat babies and possibly adults and keep the shrimp stressed and hiding. In fact, I didn't know I still had shrimp in my tank, I had added some a while back and thought I accidentally gasses them all when I fist got my CO2. I recently started seeing a couple here and there. I took all the fish out of the tank and within a day all the shrimp came out and I actually had more than 20 in the tank...lol... I added some more now I have some heavy breeding going on. I also have yellow shrimp that I am starting a new tank for.