So I'm going to buy a new filter for a 20 long and have been looking at the aquaclear 50 rated for 10 to 50 gallons it goes for around $37. But I noticed that other filters like the penguin 350 and tetra whisper 60 are also in the $30 range and are rated for 60 gallons and up so which is the better buy? I'd like to stay in the $30 range.