do tAnks need to be level?

Front to back?? How much??

I would say level it, but my 120 is not 100% level either. It has been off since install, over 20years ago.
 
unlevel creating a twist is worse than just off in one direction. Twist level is extremely important. The narrower the tank and higher the stand, the worse front-back is critical.

IMO, if it isn't level ALL ways, you haven't set it up correctly.
 
The front to back is where the water pressure could potentially blow out the front of the tank or make it bow. It isnt a huge deal if it is off by a little. You just dont want it to be off by a lot. If it is fairly close, then it is probably fine. Sometimes it is hard to get it right. Like my 29 is on carpet and I got a ready to assemble stand from petsmart. I followed the instructions and put it together. The stupid thing was different heights all over the place. The bottom support was taller than the front and so on. I got some wood shims and leveled it the best I could. It is really close in every direction, but it isnt quite perfect.
 
it isnt level on the sides but it is level in the front. if im explaining it right. if i put the level longways its centered in the middle but if i put it to level the width of the tank its in the two lines but its closer to the right.
 
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