Acrylic tank and foam questions

davis101

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Sep 7, 2009
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Well I bought the foam for my 480 gallon acrylic yesterday. The foam is 1" thick and I'm wondering if this is going to be a problem or if that is a good thickness. I was going to buy 1/2" but this was the thinnest they had in 8x4 sheets.

The second problem is that the foam is basically two 1/2" 8x4 sheets glued together and are offset from one another. How do I go about fixing this as there is a 1" gap due to the offset.

My options:

Cut the overhang off and put it in the areas that need it

Somehow cut the two sheets apart and just use one 1/2" sheet

Or take this sheet back and buy two 8x2 sheets of 1/2" or a different thickness


I guess I should mention the footprint of my tank is 8x4
 

wednesday13

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Foam is not beneficial for acrylic tanks imo, a nice level piece of 3/4-1" wood under the tank will do far more good than foam. I have 7 acrylic tanks running right on the wood,180-500gal, actually had one up on foam that leaked due to the foam crushing over time making the tank unlevel. If the tank is unlevel on the stand, shims should be used to fix the issue not foam.

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davis101

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I was using the foam to catch any deformities in the plywood sheet that is on top. It is a sanded 1/2 pine sheet, but I would prefer to have foam on it just in case there are any defects in the plywood. I will take it back and get two 1/2" sheets that are 8x2
 

wednesday13

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I was using the foam to catch any deformities in the plywood sheet that is on top. It is a sanded 1/2 pine sheet, but I would prefer to have foam on it just in case there are any defects in the plywood. I will take it back and get two 1/2" sheets that are 8x2
Again, foam will not do anything benificial and can actually cause an acrylic tank to leak as it breaks down over time under the tank weight. Use another piece of plywood on top of the existing wood, then shim inbetween the old wood and new wood to make it all level. U can even shim right under the acrylic. Foam is for plate glass bottom tanks or insulation, NOT acrylic.

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wednesday13

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Watch an episode of "tanked"...even there smart enough to not use foam under acrylic tanks. They glue a piece of 3/4" ply right to the tank bottom and shim between the wood and stand to level everything off.
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jsodwi

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I have 1/2" styro under my 750 and I'm wondering if that had caused premature seam failure. I won't use it again but cannot remove it until I take tank down and sell
 

davis101

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It seems to be personal preference as whether or not to use foam. I just did a bit of research and some acrylic tank manufacturers require foam under their tanks in order to maintain their warranties. When you use the second sheet of plywood to level the tank you suggest to add the shims in between the two sheets of plywood. In this case, how would you fill the gaps between the two sheets of plywood in the middle? You can add shims around the entire outside of the sheet, but wouldn't the acrylic sag and bend the plywood in the center?
 

wednesday13

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An acrylic tank will sagg/deform with foam under it just the same. No matter what there will still be gaps under ur tank and foam/stand somewhere. It will kinda bow to the shape of any stand eventually. Never owned a new tank, but all my 10-20yr old acrylics came with bowed unlevel bottoms. Test of time.... Too many factors too give you an unlevel product in the end, even factory made new tanks. Kinda y the mfg. "Tanked" glues the piece of wood it was made on directly to the tank bottom. Cnc tables are unlevel, acrylic itself is not perfect, wood is unlevel, floors unlevel when tanks are made, so shims are necessary in any case, more the better imo... The outer seams are what matter to keep an acrylic box/bottom from blowing, not tiny gaps under the middle floor. The tank bottom will not bow past ur supports, the bottom seams cannot seperate if you have shims all the way around if necessary. If you have an "air gap" of foam supporting the seams, it can easily be comprimised allowing seperation and tank shifting. Even if ur super careful, the foam is already breaking down by the time u get it home and onto the stand. Call it preference...i call it observe and report. Most of the people i help fix acrylic tanks with bottom seam failure had them up on foam. Ive done it myself, seen the results, so i understand. Foam under acrylic is a very popular belief, doesnt make it right.

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davis101

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Okay thanks for the input Wednesday. I'm still not 100% i know what you are meaning by shimming between the two plywood sheets. Say I have to shim the tank 1/2" on the one side That means there is going to be a gap between the two sheets of plywood and the acrylic will sag in those areas causing irregularities in the acrylic and stress points. Isn't that also a bad thing? I am not sure if I am understanding correctly or not.
 
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