I have 2 algae eaters, which is my first time owning. My question, do they kill other fish? I thought they just kind've swam around and sucked on the glass. Well, mine swim very quickly darting to and fro, going up and down on the glass at the speed of light. Are they sick? Is this normal behavior? I used to have 6 neons, but now there is only 5, I checked everywhere... My BF thinks they are killer fish, he swears he seen one eat one of the gup fry! TIA for any responses.