minorhero, thanks for you input.
Good point about fully open front doors or removable panels. I actually plan to do the same, to have easy access to equipment. Sort of deal breaker. For 120gl i would agree that the weight is significant and a middle support on 4' is needed.
Is that necessary to have double structure with middle support for a 75gl tank? I will post couple of designs and see what people say. If there are good builds already around, that are not overall, a link would be very much appreciated.
I do not have planer or jointer, but I have a table saw, and hope to mill the 2x4 nicely. But, if something at reasonable price would be available at an wood supply store, I would go that way. Maybe poplar, indeed.
What size tank are you thinking of and what size lumber are you considering?
I looked into diy stands quite a bit because I was building one in my garage. At the time I had access only to a drill and a circular saw, all of my other equipment being in storage. I got about 80% through the build before I stopped. The end result was frankly not up to my standards. I am used to working with table saw, jointer, planer, bandsaw etc. And frankly used to producing a higher level of craftmanship then my skills with just a circular saw and 2x4s were allowing. So I completely get the desire to make something better.
That said, I did not find anyone using lumber that was substantially smaller then a 2x4. There are plenty of plans for people to use plywood to build tanks. This makes sense considering that most store bought stands are just sheets of mdf. But if preferring to go a route other then plywood, then there is little out there smaller then a 2x4 frame skinned with plywood of whatever thickness the builder prefers.
However, you can certainly improvise, you are essentially building a buffet or a cabinet after all. There are lots of plans out there for those pieces of furniture and so long as you are keeping it to smaller then a 50 gallon tank you will probably be fine. Sadly I suspect no one will be able to give you more assurance then that.