I currently have a 13 gallon freshwater tank stocked with 2 swordtail platy (1 male 1 felmale), 1 pleco, and 6 japanese algae eating shrimp. I had 3 other platies in there, however they died and I'm not sure why. None of these fish are supposed to be aggressive, so I assume it's not that. I would like to add some life to the tank as only the two platies swim around. Would it be safe to add in some smaller tetras? Do algae shrimp kill other fish if there's not enough for them to eat??