I want a new external filtre for one of my aquariums (Fluval Roma 200) but i cant decide which; it is between the Fluval 205 and the Fluval 305. The boxes say for 205; For aquariums up tp 200l/40 US G (Even though 200l is about 53 US G). The 305 says; For aquariums up to 300l/70 US G. So which one should i choose?