300 gal acrylic tank over uneven stand advice needed

[Brhino]

First of all I wasn't sure if this is the best place for this thread. If not, let me know where it should go!

I've got a 300 gallon (8'x2'x30") acrylic tank that I build a stand for. I put the (empty) tank on the stand for the first time yesterday and found that the stand is slightly bowed downward in the center (I hesitate to use the word "bowed" because it implies that something is buckling under weight, which isn't the case here. It's rock solid, it's just not flat). The left and right edges of the tank rest on the stand, but in the middle there's about a 1/4" gap between the bottom of the tank and the stand, all the way front-to-back.

I was hoping that some folks with experience in large acrylic tanks could give me some advice here. I've gotten suggestions of putting a layer of floor levelling epoxy on the top of the stand, or simply using insulating foamboard, but neither of those suggestions have come from people with actual experience regarding how acrylic tanks stress and respond to situations like this, so I'm looking for expert opinions.

 

[backpack]

My glass tank wasnt perfectly level on my stand. so I picked up 100 or so shims for a toilet
at my local winnelson. they where stackable and you just hammer them in. They are sold in acrylic and rubber.
More than enough and easy to shim plus support the whole thing. acrylic tile would also be a great cheap item
if you got it on sale.

 

[KAWAMIKIE]

Styrofoam will not make up for a warped stand. It is only to make up for minor imperfections. A 1/4" gap is huge and will put uneven pressure on the tank, possibly causing failure. If you can fix it with the leveling compound it will be fine. If not you could cut the top of the stand flat or rebuild the stand.

 

[jsodwi]

What is bowed? The plywood on top?

 

[Brhino]

The plywood sits on a frame of 2x6s which sit on vertical 4x4 posts. The 2x6s must not be straight because the plywood is screwed and glued into those without gap.

The best suggestion I have heard so far is to put a new piece of plywood on top of the existing one, with precision cut furring strips between the two to ensure that the new piece is completely supported but also level. I've been advised against the use of leveling compound as it will be inflexible and brittle, so it's liable to snap if the tank or the stand shift or flex any under load.

 

[Pharaoh]

I would personally rebuild the stand or try and take off the plywood and relevel the frame underneath.

 

[Bderick67]

Yeah rebuild the stand properly, 300 gallons of water is too much to be risking on a band-aid fix.