IMO you risk far more trying to shim a full tank level then just leaving it alone, especially when the tank in question is sitting on a spongy material like carpet.
I'd be checking the bracing that supports the lids for level, I've got a custom made 90 gal that I shimmed level empty and full it "looks" off level because the top bracing isn't level, even though the tank as a whole is.
Depending on the design of the stand you can always use either a floor jack or a hydrolic bottle jack to lift enough of the weight off of the floor to slip a shim under the low corner(s) of the stand.
IMO you risk far more trying to shim a full tank level then just leaving it alone, especially when the tank in question is sitting on a spongy material like carpet.
I'd be checking the bracing that supports the lids for level, I've got a custom made 90 gal that I shimmed level empty and full it "looks" off level because the top bracing isn't level, even though the tank as a whole is.
I noticed someone asking how you level a tank...its rather simple to pop a chalk line on the tank itself at about the half way point and then use the water itself as the 'level'. By reducing the water level to half or less you cut down the possibility of damaging a seam. I use a doubled 2x4 under the top frame of the stand and then lift with the jack only till the tank starts to level. Shim the base or legs with tapered door shims...tap them in until they feel solid and then snap them off flush with the stand. slowly release the pressure on the jack and then remove the 2x4 lifting brace.
I freaked out as well after setting up my entire tank and then reading about leveling issues 2 months later. My 55g is pretty close to level when you check the front and it off about 1/8-1/4 front to back - basically the bubble is touching the line in the level.
What seemed more important to me after reading a lot of articles and forums is there is no "twist". In other words, I think it's more significant for it to be "off" by a different amount in one direction. This probably becomes more significant when working with larger tanks. I freaked out on mine, again, because it seemed to have a twist, but I discovered that the FRAME around the top is on all the way down in one corner. (WHEW!!)
