Threshold for solid contact between a stand and the tank

[InfinityARch]

Just a minor question: I've noticed there's some minute gaps between my 120 gallon tank and its stand where I can see light passing through the gap if I put my eye directly up against the stand-tank interface. From what I've read, you only need truly solid contact at the corners, but I'm not sure how to positively test that. It certainly looks like the corners are in solid contact, but I'd prefer not to eyeball it.

I ran a credit card (which is 1/32" thick) around the rim, and found some gaps near the middle of the tank, but none that the card would fit into near the corners. Is this a good enough test, or should I try and find something even thinner?

 

[Steve_C]

If its glass then usually just the corners need to be supported. CC is a tad thick for testing like that, you want full contact in the corners where even a normal paper wont slide under it without having to work it into there. Long as the corners are that way and its just the center where there's small gaps then you should be fine if its a glass tank.

 

[InfinityARch]

I'll try again with a sheet of paper then.

 

[BIG-G]

This is assuming the stand is leveled side to side and back to front.
slightly out of level in any one direction would probably be okay as long as there is no twisting.
So you definitely don’t want any two opposing corners out of level.

 

[skjl47]

This is assuming the stand is leveled side to side and back to front.
slightly out of level in any one direction would probably be okay as long as there is no twisting.
So you definitely don’t want any two opposing corners out of level.

Hello; This for sure. You do not want out of level at corners. say at right front (RF) to left rear (LR) What I mean is if you drew an X across the top of the stand from corner to furthest corner. The line of the X should be level as well as side to side and front to back. Out of level along the X can mean a twisting that the glass may not hold up to.

 

[InfinityARch]

Hello; This for sure. You do not want out of level at corners. say at right front (RF) to left rear (LR) What I mean is if you drew an X across the top of the stand from corner to furthest corner. The line of the X should be level as well as side to side and front to back. Out of level along the X can mean a twisting that the glass may not hold up to.

To the extent that I can tell with my beam level, it's dead level left to right, front to back and across corners. Should I be using a tape measure and getting the water level at the ends instead, or is the beam level more accurate/good enough? I think it might be like 1/32" low in one corner, but I can't tell because that's between the lines on the tape measure. I've been measuring from the bottom of the tank rim to the water line btw, not the floor to the water line.

I'll have to see if the shims compress under the load, but they're wood/plastic composite and rated for 15,000 lbs force each, and I didn't leave any gaps between shims at all, which I've been told is overkill.

I assume the structural members in the floor will settle somewhat when it gets to full load (right now it's about 1/4 full), but it's perpendicular to the joists which seem substantially overbuilt to begin with. The span tables and online construction resources I looked at suggest to me that they're just short of being able to hold a uniform 60 psf load compared to the 40 psf building code. I have no idea why it was build like that but I'm not complaining because it means I have a theoretical safety factor of around 1.6 with the tank placed where it is, which is within the norm for structural engineering, even if 2.0 is preferred. (and I included a bunch of extra weight, including myself to be extra careful)

One possibility that concerned me is that there might be a weakened joist that's caused the floor to deflect in the first place, but after going around the entire room with my level it seems like there's just a mild uniform grade in of about 0.15° rather than a low spot, which is indicative of the foundation settling (or a deliberate design choice, but I can't imagine why you'd do that), and as far as I can tell not an issue as far as I'm concerned as a renter intending to live here for maybe 6 years (don't worry, I have renter's insurance, a rider policy covering the tank in the event something goes wrong and written approval from the landlord on the condition that I get such a rider policy) with such a mild grade.

The tank is also sitting in a corner between two load bearing walls placed such that the edges of the stand are resting in the midpoint of of the tributary area of the structural members to its left and right; I'm not sure if I should have done that, or if it would have been better to position the ends of the stand to be as close to being directly on top of joists as possible, but while it would be annoying to relocate the tank it's doable.

 

[skjl47]

that I can tell with my beam level, it's dead level left to right, front to back and across corners.

is the beam level more accurate/good enough

Hello; here is the web address link of an article that talks about the floor support issue.

Around 1/32 inch is close and I just use a long level only. I get why you are being so careful and do think care needs to be taken. From your posts it seems you have taken most any precaution I can think of. I don't plan to put a tank the weight of a 120 gallon on a floor with wood joists unless I add some support under the floor, but some may have more useful experience.
One story; I placed a 55 gallon in a room over my basement. I have 16 inch on center joists and placed the 55 near the center of the joists running parallel which is the worst spot. I figured a 55 was not heavy enough to matter much. Well nothing broke or collapsed but when I walked thru the room the water would slosh a bit. I fixed some minor bracing underneath and cured the sloshing. I might go with a 75 gallon in a corner running perpendicular but that is about the extent of my bravery. Not saying you cannot do a 120, just have only ever kept a 120 on a slab floor myself.


http://badmanstropicalfish.com/articles/article28.html

Good luck.

 

[Ulu]

Having a big tank that is 1/16 of an inch out of plumb it's not a problem but having a tank that does not have full contact bearing is a bad choice.

Once your stand is shimmed up to where it is square, you can apply a bedding compound to the top of the frame and then seat the tank in that, fill it up enough that you can tell that it's level and settled, and let it dry. You can also bed the stand to the floor and then remove those shims later and fill in where they were.

What type of bedding compound you use depends on what kind of floor, stand and tank you have, so do your research.

 

[InfinityARch]

Having a big tank that is 1/16 of an inch out of plumb it's not a problem but having a tank that does not have full contact bearing is a bad choice.

Once your stand is shimmed up to where it is square, you can apply a bedding compound to the top of the frame and then seat the tank in that, fill it up enough that you can tell that it's level and settled, and let it dry. You can also bed the stand to the floor and then remove those shims later and fill in where they were.

What type of bedding compound you use depends on what kind of floor, stand and tank you have, so do your research.

Good suggestion as far as dealing with the gaps between the rim and the stand. It's currently got water in it since I was testing the plumbing, but I found a leak in the sump I got with the tank so I've already started disassembling it.


OTOH, my tank has an extremely tall rim compared to the plastic rims used for supporting a normal tank, so wouldn't a Styrofoam mat work for this application, as long as the rim is too tall for the bottom glass to come into contact with the compressed mat?

 

[Ulu]

Well styrofoam mat would be better than discreet shims. The whole idea is that whatever you use should provide continuous uniform bearing.