i put a 6 inch piraya and a 8in. cariba in a 75 gallon tank. the cariba has been beatin the hell outta the piraya for a lil while qht do i do?, the tank has plenty of space, plenty of filtration, plenty of places to hide. the cariba would rather attack the piraya then eat...but the piraya swims right up to him..? would a 90g fix this??