I mentioned that 4x4's should be used because of the over kill. I have looked at the stands at the LFS and as a builder I would not want something that frail holding up 150 Gallons of water in my house. I know of friends that have these tanks and over time you can move the tank and the stand looks like it will come apart, they rack back and forth. Again a 4x4 leg may be overly stout but it is better safe than sorry. Your tank gets some of its support from the double 3/4" ply wood. Most builders will use 1 sheet and depend on the frame to support the weight. Plywood will keep the frame from racking, 1x4's supporting 3400 lbs would make me uneasy.