Will it be okay??

Aight so I'm finally getting back into the hobby long story short I built myself a stand for my 20g long aio set up and the tank fits good and looks great but isn't 100% flat on top of the stand will the rim of the tank work itself out once I get water in it or should I put a foam board under it... Any suggestions???

 

I took a better picture, that gap is only on the one corner. At the corner I can squeeze a penny in however the side gets closer to a 1/4 of an inch

 

Sounds like it's high in the middle?

 

I think it will be fine to leave it IMO ..
After water and rock it will probably be close to 110 pounds or so ..Now if it was 1100 pounds i'd make sure it was flat.

 

just out of curiosity, why is it doing that?

 

I would guess there is a slight warp in the wood .

 

Personally, I would not trust it. Any lack of support will create stress for which the tank was not built to tolerate, regardless of size or weight. I'd definitely recommend using a foam board under it.

 

Yeah the wood is slightly warped down in that spot causing it to not be fully supporting it, I thought about using foam I'm just not sure how that actually works

 

I was thinking about putting a cork board under it , or maybe trying to get a flat piece of plywood that would match the outline of the tank

 

The cork sounds like an interesting idea. The cork out foam should be about 1/2 inch thick to allow for compression at the high spots. If you use plywood, it will eventually take on the same shape as what is under it, unless you add shims in the appropriate spots.