What size would you recommend aquarium

well, let me know they really are decent lights for fish only and some corals... see my 6' long thread to see pics of the lights and how good they work. I'm looking to go to mh's so I can get more diverse corals

 

I'd stick with the 125. There is a lot more ITO aquascaping you can do. I'd much rather go out than up. It is more expensive ITO the lighting, of course, but if you have the means, I would stick with what you already have.

 

I would question even exactly how much you will actually save. for one, you will need longer lights. But for the other, your going to need much more powerful lights to penetrate deeper. If you add in the cost of the new tank, you probably wont be saving anything in the full spectrum of things, or possibly even lose some. Second hand tanks aren't worth hardly anything. About a dollar a gallon seems to be the reasonable going rate. A lot of people can't sell their tanks because they don't realize how much they depreciate in value as soon as the first owner walks out the door with them.
Also, in general, longer, shallower tanks are better. Less powerful lights will be needed to penetrate effectively, and fish don't swim up for excersize, they swim side-to-side. You'll have much more room for your creatures with a longer tank.
Just my 2 cents

 

worse then a car lol. thats why i by used.