I believe he said he was looking at a 210g tank which is 6 foot long so a 90g tank that is standard is 4 foot gives you 2 feet of extra room for a shelf or 2 for putting your chemicals and dry good on. In the 90g you can section off a area that comes to 10 g for your ATO water. Now you you guys see where I am going with this everything in one area. you can make a sump with a fuge on top that uses only 1/3rd of the area and under you Ty-wrap some egg crate together for things like sponges to grow on and mini feather dusters, this polishes the water for you. I have a acrylic sump built that employ-es this idea and looks good tanks up less space and I have no worries of overflow. it is 20 inches deep but only 10 of it is for the sump and the top 10 for the fuge which only take up 1/3 rd the area on top. that leaves almost 20g for over flow.
I have not installed the sump yet but did a wet run of it and it works well.
Bill