1x6's strong enough for a 55g stand?

[hsd]

I'd recommend putting on edge though. 1/6 flat will bow really bad even at 16" O.C.

I may eventually put some board on the sides/back. Was planning on putting in 2 additional legs in the center as well. Just didn't want to build anything too bulky/heavy that I would have a hard time moving it later.

 

[mdb_talon]

It's way overkill. 2x4s will work, even 2x3s. You're only talking 500 to 600 pounds of tank and water. 1x6s will add unnecessary weight.

1X6 is less weight than 2x4 and the same as a 2x3.