For the first year or two, I had the 75g up top and nothing on the bottom. The stand is a little wobbly that way if you push against the tank, etc. I was worried about it and contacted the manufacturer with my concerns. They got back to me right away and claimed they weight tested this stand with 1500lbs per shelf with no signs of fatigue.I read a couple of reviews on this stand and ppl are saying its wobbly and wouldnt trust it to hold anything bigger then a 75, did you have any issues with it not being sturdy?
Once I added another tank to the bottom, the stand firmed right up. I would definitely buy one again. Not for a carpeted floor, but ideal for hard floors. There is 12" of space above the lower tank with a 75 (or 55) on the lower shelf.
I added some floor jacks in my basement under this setup because the setup runs parallel with my floor joists.