Uneven Stand Top

[ndrwater]

Can I fill up those area with wood filler? And then set the 3/4 plywood on top

Filler isn't structural. You could however, fill any gap AFTER making sure the top was flat.

 

[Danh Ngo]

Filler isn't structural. You could however, fill any gap AFTER making sure the top was flat.

all the edge are level, but the top is kinda bow a bit at one corner. It may create a little gap undernearth the new top that I put on. That’s what I’m a bit concerning
The pic below, it is not a gap at the edge

 

[ndrwater]

This is a eurobrace tank yes? No bottom trim? If so, then the foam mattress you have should take care of this no problem.

 

[Danh Ngo]

This is a eurobrace tank yes? No bottom trim? If so, then the foam mattress you have should take care of this no problem.

Rimless, no bottom trim, but not eurobrace

 

[ndrwater]

Rimless, no bottom trim, but not eurobrace

Same diff. You should be just fine. If it does indeed still haunt you, I would use a harder filler like Bondo to fill the low spot. Sanding and a nice straight edge would confirm that you were then bang on flat.
A 1/6" hollow in an area away from the edges, in conjunction with the aforementioned mat, should handle this with no issues.

 

[Danh Ngo]

Same diff. You should be just fine. If it does indeed still haunt you, I would use a harder filler like Bondo to fill the low spot. Sanding and a nice straight edge would confirm that you were then bang on flat.
A 1/6" hollow in an area away from the edges, in conjunction with the aforementioned mat, should handle this with no issues.

Thank you for the info