Go for it! That extra 6" in the 120, even if the overflows aren't in the corners, makes a world of difference for aquascaping.
Yeah, but the overflows come off the wall like 4''. He would still be stuck pushing his rock closer to the front wall on both sides since the 120 is a dual and not a single. If you still have to buy a tank, get the 120 over the 90. If I had the tank up and running already, I personally would not change it for this reason alone. Just my opinion.
I just went from a 55 to a 140. Same footprint as a 120.The shop I got it at gave me the same price as a 120. I made the switch 1 month ago and everything went pretty smooth. I had 70# of 5 year old live rock and added another 70# of Marco rock which is now beginning to get the coraline growth. I started with a new sand bed which I seeded with about 1 1/2 cups of sand from my old tank. Before I made the switch my NO3 was about 70PPm within one week the new tank was down to undetectable that was a quite a surprise. You might want to look at the price difference between the 60" 120 and a 60" 140.
Is your 90g 60"?
I was also originally trying to decide b/t a 90 and 120. I personally think the 120 is one of the best sizes for a SW tank. Of course I will go 300 DD next I went with a 120 with custom overflow in the center of the tank. So much more room for aquascaping that way IMO. I hated the twin overflow 120 layout.
Link to build if interested in the plumbing etc.
http://www.reefcentral.com/forums/showthread.php?t=1805337
<a href="http://www.flickr.com/photos/14049800@N00/4213004607/" title="New tank. 120 gallons with custom flow by RVAE34, on Flickr"><img src="http://farm3.static.flickr.com/2488/4213004607_0497a4a232_b.jpg" width="1024" height="684" alt="New tank. 120 gallons with custom flow" /></a>
<a href="http://www.flickr.com/photos/14049800@N00/4213770178/" title="New tank. 120 gallons with custom flow by RVAE34, on Flickr"><img src="http://farm3.static.flickr.com/2673/4213770178_74ed793d35_b.jpg" width="1024" height="684" alt="New tank. 120 gallons with custom flow" /></a>
Thanks everyone. Good discussion. My issue is not the 6 inches or the aquascaping. (and my 90 is down right now due to a move) But the issue is I was never very happy with the flow in the tank and always thought I'd be better off with a dual overflow. I have s special spot to reset the new tank but a 6 foot wde tank won't fit. I could do 5, but found a 120 (4X2X2) that has dual overfloows at a reasonable price. So do I get it or stay with the single overflow?
Yeah, the 90 is torn down already due to a move. Currently working on the "fish room" behind the tank wall where the tank will be. I hope to set it up as successfully as I did at the last home, but thinking I could improve things some...I have an opportunity to get this new tank at a good price even though I don't really need to.