Thank you for making that very important distinction. I totally neglected to mention what I was shimming. I shimmed the stand (an old dresser), and not the tank, to get the tank close to level.

Speedy fingers!

I went to butter my toast In the middle of writing my reply and didn't see yours.

Yes, toast for supper. This hobby is leaving me broke. :lol:

Good stuff, it's also a good idea to check if the surface the tank sits on is perfectly flat, if not you should use some thin foam or rubber under the tank to even it out. If it's already running you can't really do much though.

I should add that leveling a tank is a good idea, it's an easy task and everything will look and work better but being off won't cause it to break, that's just silly.

I can fit a piece of paper between the trim and the stand on the front over a length of around 6". I missed that earlier. I checked that the centre of the tank was in contact with the stand. The gap is to the left of centre.

I've got around 15 gallons in the tank so far. Is it important enought that I should drain it and use the foam?

If so, could I use layers of laminate flooring underlay? We've got piles of scraps of that (Hubby installs wood floors for a living).

My 175g has always been out of level currently by about 1/2" both front to back and left to right. The tank has Been moved several times since I got it about 4 years ago I'm pretty sure that the guy that had it before me had it out of level. The stand is flat on both top and bottem so the entire thing is tilted.

Yeah if you're just filling it and you got 15 gallons in there, it would be wise to drain it seeing how it's possible some of the tank may not be supported completely. Foam underlay really isn't ideal as it's not very rigid but it would be better than nothing, just make sure it's even and not making things worse. What can work quite well that is readily available and not an eyesore is the one sided black foam tape. It's used for insulating things like attack access hatches and other generic applications, available at pretty much any hardware store. You can just stick to bottom of the tank frame itself.

I'll see if I can find the tape. TY!

Woah! Placed our new display tank on its stand last night. There is a very significant gap (1/8" or more in some places) between the black plastic trim and the stand on three sides of the tank.

I've found a couple of different types of foam tape. I have found "expanding" foam tape (an automotive product, but I think it is too thick), and weather stripping foam tape (in various thicknesses, and open and closed cell). Is one of those types of tape what I should be looking at?

This is only my opinion, and anyone else who says otherwise is not connected to me ... blah, blah, blah, ......

I am very concerned about what you have said with your gap between your stand and tank
Do NOT try to fill the gap with something ....
Your stand, IMHO, should be as tight a fit to your tank as possible ....

IMHO, no foam will ever alleviate / fix compression of our tanks ...

Put your tank on it's stand and let the carpet settle, 1/2 day, all day, all weekend, whatever .... fill it and let it settle
Next, put RO water in it to the full line and level it when it's full ....
Now you can play with the level limits ...

The most rigid tape foam you can get is fine, you don't want an expanding foam or anything that compresses too easy. A better choice given the gaps being noticeable and what most people typically use is the 1/2" pink rigid foam from the insulation department but it's pink so not always the nicest thing to look at unless you cover the edges with tape or something. Ideally the stand should be better but 1/8" isn't terrible, rigid foam will compress with the tank and water weight enough in the right places to seal any gaps in support.