I am redoing my fish room in the summer. I am planning on making a new rack that can hold up to 4 30 gallon but most likely will only have 2 30 gallon on the bottom, a 20 gallon and then 2 10g. I currently have all my tanks with HOB filters but it takes up a lot of outlets. Would changing to sponge filters be the best idea and if so what size would I get for each tank? I went on amazon but couldn't tell what size they were. If you have any recommendations links to Amazon would be very helpful!