levelling/floormat/stand problem

zob

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I've had this home made 110 gal tank with stand for 35+ years, and it was 2nd hand when I got this. A couple of months ago I replaced it with a new 110 gal with the same dimensions.
The old tank sat on 10mm plywood + 20 mm hardboard + 20 mm styrofoam. All in poor shape and I replaced it with a heavy 18mm waterproof underlayment plate and the manufacturer of the tank insisted on using a 5mm foam mat instead of styrofoam. I checked the beams of the stand (8x 65x45mm) it was level, and once the tank was on it and filled, everything seemed fine.
After a month or 2, I noticed the pressure on the foam mat is every uneven, from ±2mm on the edges till ±5mm in the middle.
DSCN4107.JPG DSCN4108.JPG DSCN4109.JPG
2nd pic shows the right corner on the right, with about 50 cm of the tank
3rd pic shows the side of the tank, with that right corner on the left. The difference in the mat is about 2mm on the left up to 4mm on the right.
Is this normal, or is the stand sagging or something? How thick should the bottom plate be?
It is to be noted as you can see in the first pic, the tank/bottom plate has about 40mm hangover from the supporting beam. This used to be ±100mm as the previous owner had a really thick backdrop between the tank and the wall. I don't quite know what to make of this, having used the stand for so long, I thought the new plate and position was an improvement, if the beams are now bending it seems extreme to me, or maybe it was always this way and the bottom plate needs to be thicker, or more foam?
Your thoughts and comments are appreciated !
 

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I've had this home made 110 gal tank with stand for 35+ years, and it was 2nd hand when I got this. A couple of months ago I replaced it with a new 110 gal with the same dimensions.
The old tank sat on 10mm plywood + 20 mm hardboard + 20 mm styrofoam. All in poor shape and I replaced it with a heavy 18mm waterproof underlayment plate and the manufacturer of the tank insisted on using a 5mm foam mat instead of styrofoam. I checked the beams of the stand (8x 65x45mm) it was level, and once the tank was on it and filled, everything seemed fine.
After a month or 2, I noticed the pressure on the foam mat is every uneven, from ±2mm on the edges till ±5mm in the middle.
DSCN4107.JPG DSCN4108.JPG DSCN4109.JPG
2nd pic shows the right corner on the right, with about 50 cm of the tank
3rd pic shows the side of the tank, with that right corner on the left. The difference in the mat is about 2mm on the left up to 4mm on the right.
Is this normal, or is the stand sagging or something? How thick should the bottom plate be?
It is to be noted as you can see in the first pic, the tank/bottom plate has about 40mm hangover from the supporting beam. This used to be ±100mm as the previous owner had a really thick backdrop between the tank and the wall. I don't quite know what to make of this, having used the stand for so long, I thought the new plate and position was an improvement, if the beams are now bending it seems extreme to me, or maybe it was always this way and the bottom plate needs to be thicker, or more foam?
Your thoughts and comments are appreciated !
How are your stand supports inside the stand?

Might the underlayment be compressing unevenly?

My stand was used when I got it, not nearly so old as yours, but one support had rotted entirely away and another was iffy. Before we filled our tank on that stand, we replaced those. We also reinforced other internal stand areas.

Under our tank's display stand, we built out a level floor box as our room is a converted porch so there is slight slope. We didn't want to use shims, so we ripped 1x1s down. Where the display stand's downwards supports come down, we used 4x4x cross grain to ensure no compression. With all the thought that went into 'engineering' our 'shim' (6'x2' box with cross bracing, all level, painted while (its that tiny strip under tank in my photo)) it makes me think if not stand supports giving way then perhaps underlayment.
 

Fish Think Pink

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How are your stand supports inside the stand?

Might the underlayment be compressing unevenly?

My stand was used when I got it, not nearly so old as yours, but one support had rotted entirely away and another was iffy. Before we filled our tank on that stand, we replaced those. We also reinforced other internal stand areas.

Under our tank's display stand, we built out a level floor box as our room is a converted porch so there is slight slope. We didn't want to use shims, so we ripped 1x1s down. Where the display stand's downwards supports come down, we used 4x4x cross grain to ensure no compression. With all the thought that went into 'engineering' our 'shim' (6'x2' box with cross bracing, all level, painted while (its that tiny strip under tank in my photo)) it makes me think if not stand supports giving way then perhaps underlayment.
with all that said, perhaps the foam mat is doing what it should, and maybe you've got no worries... defer to others on this thought, as foam mats are outside my experience
 
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zob

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Thanks for your replies, someone also said that it could be normal for the foam mat, but I am old my tanks either had styrofoam or open metal stands so I don't know.
I checked the stand supports, they were fine... 4 of them on each side.

Might the underlayment be compressing unevenly?

I have thought of that as well, but I don't know if it is possible? It was said to be about the highest quality available, 18mm, waterproof and made out of birch. It is normally used on trailers for bottom plates.
 
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did you check to make sure the stand is level. With a wood stand that’s as old as this one the weight of the tank could be causing it to deform. If I had to guess I would say the front right side of the stand is the low spot. The tank doesn’t compress the mat evenly because the glass isn’t flexing(for now). Check the level and shim accordingly. The Matt does help, but I wouldn’t count on it to compensate for major defects. Especially when the fix is as easy as a pack of shims from the hardware store. Allot more economical than a flood. Good luck. I hope everything turns out well
 
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zob

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When you put a 2 ft level on it it says it is level. I would have thought the right front spot was the low spot as well, but I measured the water column and it is actually 2mm lower there as on the other side (5 feet). (??)
 
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zob

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How does the foam work exactly, does it still spring back after being compressed for a long time or can it only be used once?
 

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