Top of tank stand is slightly uneven. Ideas for a fix?

[Seisage]

I'm almost done making a DIY tank rack for two tanks. Despite my best efforts, I think tightening the screws caused slight shifts in the positioning of the 2x4s and so the top "shelf" is slightly uneven. I tested it with an empty tank and there's just one corner that doesn't quite touch the frame. This continues for most of the way along the front edge of the tank, but the opposite corner is fine. I tried sanding down a couple spots that seemed to be the issue, to no avail.

I've looked around on some other forums and from what I can tell, the most important thing is that the corners are supported and that the edges aren't as important. The gap itself is 1/16" (~1.5mm). I figure I can just shim that corner underneath the tank, but does anyone have any suggestions for materials? I could get wood or composite shims, but I'm wondering if I might even be able to get away with some of those felt pads that are meant to go underneath furniture.

Edit: I guess I could also just get a piece of plywood to go on top. It might look nicer than shims, but it would definitely be pricier.

If it matters, the tank that'll be going on the top here is a rimmed 25gal.

Edited January 19 by Seisage

[Fish Folk]

All of my tanks are tilted ever so slightly. Super triggering! Eventually, I discovered that my entire basement floor is tilted!

Once full, there’s going to be ca. 250 lbs of weight on that shelf from that tank alone. Spaces might disappear…

[Seisage]

On 1/18/2024 at 4:36 PM, Fish Folk said:

All of my tanks are tilted ever so slightly. Super triggering! Eventually, I discovered that my entire basement floor is tilted!

Once full, there’s going to be ca. 250 lbs of weight on that shelf from that tank alone. Spaces might disappear…

Yeah, I know a lot of floors are inherently unlevel! My issue here is that the surface the tank will be resting on is uneven, hence just the one floating corner. Otherwise, the tank is level. But it's true, the weight of the filled tank may even things out. That said, I feel like 1/16" is just enough of a gap to where I feel that may be unlikely. We'll see! I'll wait to do any shimming until after the tank is on the stand and filled, but if there's still a gap afterwards, what would you recommend shimming with?

[Fish Folk]

On 1/18/2024 at 8:20 PM, Seisage said:

if there's still a gap afterwards, what would you recommend shimming with?

You could glue a measured shim on. They come in packs with varying sizes at hardware stores.

But honestly… I always lay out a fitted board for the tank to sit on. Not a cheap option, but I prefer it.

Edited January 19 by Fish Folk

[nabokovfan87]

On 1/18/2024 at 5:20 PM, Seisage said:

We'll see! I'll wait to do any shimming until after the tank is on the stand and filled, but if there's still a gap afterwards, what would you recommend shimming with?

I use the plastic, molded shims. Higher weight load and you get about 40-80 of them for fairly cheap.

Composite Shims Leveling Wedges, 36 Pack 8-Inch Plastic Shims, Extreme Load Support for Furniture and Appliances, Easy to Snap Door Shims, Window Shims, Toilet Shims, Table Levelers and More - TUFFBOY https://a.co/d/fExg1kQ