I found something on another site,I want to copy paste here and get thoughts on.It makes perfect sense,and I never thought of it myself.

Quoted from cichlidfinder:
"When deciding tank stocking we often talk about tank foot prints. Alot of people get confused about what we mean. Here is a perfect example. This tank is a 29 gallon tank that has the same foot print ( Length and Width ) as a 20 gallon long.

Therefore the water surface area ( Where all the gas exchange actually happens )is the same in both tanks.

Also when considering fish size we need to look at length and width over depth. Therefore the two tanks should be stocked the same even though one has 9 extra gallons.

The advantage of a 29 vs 20 long is the extra 9 gallons of water means the tank will react slower to any sudden changes in water chemistery if something should go wrong.

P.S. When talking to others about stocking lighting etc. we generally assume standard tank sizes. Therefore if you confuse a 29 with a 30 and say whats an extra gallon matter? It means alot. "

Post in full here:30gal tank. pic spam - UltimateBettas
Its the last comment.

I think its a good bit of info and thought I would share and see what others thoughts on this are.

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http://bountifulbettas.blogspot.com/

"Come to the dark side....we have cookies...and filters/heaters/and water changes!"

With planted tanks the surface area is simply not a consideration.

Because the carbon dioxide is consumed by the plants and oxygen returned as well.

my .02

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fw leiden since 1979, fo salt since 1979, mixed reef 55g 2002-2009. Strong emphasis on the tank taking care of itself. Balanced with plant life, no water changes, tap water, no filters in FW. Only dosing calcium, alk, mag in marine reef tanks. http://www.aquariumforum.com/f15/my-...ods-26410.html
recent tanks (till 2009) 7 years- 10g FW leiden 7 yrs, 55g mixed reef 7, 2 yrs, 20g FW leiden, 10 g fw leiden , 29g mixed reef, current tank 55g leiden