I would replace the OSB panel on the end (and top?) with real plywood, that OSB looses any structural strength pretty quick, especially if it gets wet, other than that looks good.

Appreciate all the comments thus far!

I agree to replace the OSB with plywood. Construction grade is fine. What are you doing with the long sides? How will they be finished? They need to be skinned or something because the stand needs to be braced to prevent the top shifting away from the wall. The center "wall" is unnecessary. I would also want to increase strength on the top...the way it is will allow a fair bit of sag between the verticals. Maybe add another 2x6 (or 2x4) to the top plate alternating the lap on the corners?

The top and front panels are plywood. Also they have since added a plywood panel spanning the length of the stand attached to the center verticals.
The sides are drywalled, any issues with that? Thanks!

My two suggestions were front/back cladding and to orient the top pieces on end. Sounds like it may be too late to change the top pieces but laying them on their faces doesn't do much. You do have a ton of verticals in there so maybe it won't matter but that's my suggestion.

Ur stand looks very sturdy...... and to be honest, a little overkill. There's a lot to gain in terms of storage under the tank if you to build it with less vertical supports. I personally would have gone with 6*2x6 for vertical supports - two on each end and two right in the middle. I would then double up 2x8s to span the length on both sides. The space I would gain under the tank I would make into cabinet space for storage. That just my 2cents.

I agree with Chin Lee. You could park a Mac truck on that stand. There are way more studs than is necessary. I'd take some out to create more storage space.

+1 on that. I'd have done 2x6's doubled-up for headers with 1 support in the middle. I'd put cabinet doors on both sides of the peninsula for storage.

Nothing wrong with the way you're going; I think you'll miss the storage for fish-related stuff.

Got some great feedback thanks all. The picture doesn't show but There is a fairly large closet access area on the one side of that stand. Plus itll be plumbed to basement.kinda worried about the drywall tho.

The gypsum board (drywall) will be fine. It helps holds houses up, so it should hold your tank up. ;) Although don't be fooled, the end that I can see in the photo is OSB (chip board), not plywood. Plywood stands up to wetness much better. How do they plan to tie in the OSB end with the gypsum board? Trying to mud over it won't work...the OSB will expand and contract like any other wood, and the gypsum won't. The corners, and any joints will crack.