Gaps Between Stand Top and Tank Rim

[Hugh Mann]

Evidently I suck at carpentry, or I need a new straight edge. Or I am an idiot. Perhaps a combination of thereof and more besides.

Anyways. I used a 3/4” sheet of nice, very flat, finished plywood to top off the stand I built for a 230 gallon. It’s a rimmed tank, so I know I don’t need it, but for strength, aesthetics and the lumber used for the frame isn’t exactly flat and square either. Best that was available. Evidently it is not in fact, as flat as advertised. Checking with a feeler gauge, I found that about 40% of the rim is not touching wood. Gaps range from 0.006” to 0.05”, most notably two corners are not supported.

I imagine this is rather problematic. The obvious answer is remove it, it’s going to cost me about $150, as I have to pay a company to lift it for me (even if I have the suction cups, I cannot get enough friends in the same room at the same time), and my budget is basically maxed out. I also can’t guarantee the top frame itself wouldn’t be a repeat of the Battle of the Gaps.

So my main question here, is, is there anything I can do about it? Is it even a problem? With the weight of the tank, will it compress the plywood and level itself? My first thought was shims under the plywood, but I feel like that is asking for problems down the road.

 

[Jekyl]

They make tank leveling pads. Something to look into to see if it will correct it.

 

[Hugh Mann]

They make tank leveling pads. Something to look into to see if it will correct it.

It’s my understanding those aren’t great to use on rimmed tanks. Something about they can apply pressure to the bottom glass?

 

[Chrisv.]

BRS sells neoprene pads

 

[WVNed]

I would not worry about that at all. The weight of the tank will settle into the soft wood and compress all of it together.
The gaps will go away.
I am building one myself at the moment for a 180.

 

[WVNed]

How did you fasten the plywood down? Hopefully there aren't and screws under the tank rim that will protrude as the wood is compressed.

 

[Hugh Mann]

How did you fasten the plywood down? Hopefully there aren't and screws under the tank rim that will protrude as the wood is compressed.

I did use screws, but they’re countersunk pretty good as I did expect the wood to compress over time.

 

[WVNed]

I don't think it will compress more than 1/8th inch.

 

[Doctorgori]

yoga mats from the dollar stores is what I use. But I Agree if not too big it will settle in

 

[RELLIK-REEF]

I built a stand for our 180, I even double sheeted the top and still had the same issue. It's not the plywood it's the 2x4s or whatever you used for the stand. I checked the same way you did. I figured it would settle in place, filled it with water and it was perfect. 5 years later still no problem.

 

[WVNed]

There is a mat under my 240 because CustomAquariums said too but there will be nothing under the 180.
The tank will be sitting on its perimeter.

I am not scared of the big glass boxes like I used to be. You watch people roll them and flip them end for end getting them in. They are pretty strong. You just don't want a hard high point like a screw becoming a stress point to start a crack in the glass.

 

[fishface NJ]

Never use a pad under a rimmed tank. It will cause problems with the under glass. The tank will be fine on the stand

 

[Hugh Mann]

There is a mat under my 240 because CustomAquariums said too but there will be nothing under the 180.
The tank will be sitting on its perimeter.

I am not scared of the big glass boxes like I used to be. You watch people roll them and flip them end for end getting them in. They are pretty strong. You just don't want a hard high point like a screw becoming a stress point to start a crack in the glass.

I figured they were built tough, but never hurts to check, right? Makes sense these things are built with huge safety factors in mind, as the consequences of failure are… substantial.

 

[Chrisv.]

Never use a pad under a rimmed tank. It will cause problems with the under glass. The tank will be fine on the stand

Didn't realize this could cause an issue. Any idea why this is the case?

 

[Hugh Mann]

Didn't realize this could cause an issue. Any idea why this is the case?

Rimmed tanks are designed in such a way the entire weight is on the rim, as it’s the only part touching the stand. Using a levelling mat, the rim sinks into it until the mat is also touching the glass on the bottom of the tank, putting pressure on the actual glass.

As to why having the weight distributed across the entire bottom is bad, I can’t say.

 

[EeyoreIsMySpiritAnimal]

Rimmed tanks are designed in such a way the entire weight is on the rim, as it’s the only part touching the stand. Using a levelling mat, the rim sinks into it until the mat is also touching the glass on the bottom of the tank, putting pressure on the actual glass.

As to why having the weight distributed across the entire bottom is bad, I can’t say.

It's not bad if the tank is constructed to be supported that way.

 

[EricR]

So,,, the problem is that the top of the support frame isn't all in one plane, correct?
Then the plywood just bent to conform to the frame when screwed down, I assume.

Not saying there will ever be any problem but, if it were me, I'd reconsider shimming between the frame top and the plywood in the low spots, if possible.