Stand for a 600L (160 gal) glass tank

[rugato]

Hi!
I've been taking a look at this post from 2018 about a wood stand for a very big and heavy aquarium.

I'm currently trying to design a stand for my own glass 600L (160 gal), with dimensions 200x50xH68cm (~78x20xH27 in). Rated capacity 600L, so in the ballpark of 1800/2000 lbs when full and dressed.

As I haven't got the first clue about structural analysis and the bearing capacity of wood, I thought I would ask for some help here instead of making potentially catastrophic mistakes. Taking as a starting point this final revision from that post, I am considering the following changes:

1. The structure needs to be 56cm (22") high
2. I need to build it with locally available wood sizes. The most common diy wood in my area is fir, and the closest thing I found to dimensional 2x4 and 2x6 (i.e. 1.5"x3.5" and 1.5"x5.5") is 35x95mm (1.38"x3.74") and 35x145mm (1.38"x5.71"), so a bit less thick and slightly wider. Do you think this significantly changes the weight bearing capacity? (I'm quite a bit lighter than the other user's aquarium)
3. It's perfectly ok for me to have a center beam in the front, and 2-3 beams in the back. Does this mean I can use the smaller size wood for the entire build, now that the horizontal beam runs for max. 1m (~40") continuous instead of 2m (~80")?
4. The structure will sit on a slight slope of 1.1° along the 50" dimension. Which translates to a 1cm (~0.4") height different between the back and the front of the aquarium. This is not a lot, but I would nonetheless like to compensate for it. My idea is to have the long base beam in the back cut to 1cm/0.4" less, and the 5 short base beams to have a sloped cut along the bottom to follow the slope
5. Given the slope, I would think that it's a good idea to also have a plywood sheet under the stand, to distribute the load evenly and have maximum friction. Is 0.35" a good thickness for that? And do you think I can go with 0.35" for the sheet under the aquarium as well?
6. I will also probably brace the entire structure to the wall, just to be on the safe side.

Here's a drawing encompassing most of the above points:

As a side question, what does "skin the stand to keep it from racking" mean, in practical terms?

 

[shwareefer]

Fir is strong. Your wood sizes are fine.

I would still use the larger size wood for the top rail.

I would simply build the stand square/true and then shim under it for floor level.

Plywood top is fine, thickness doesn't really matter.

The points I marked can still roll if your drunken friend falls into the side of your stand for example. Skinning it removes that potential motion. Your idea to attach to the wall does the same thing. If you have concerns, adding construction adhesive at your wood joints makes the stand very strong.