New tank

I like these square washers, the big ~2"x2" ones, you can get them at Home Depot. You want the ones with Zinc.

as long as the stand is rigid enough not to flex, then shimming isn't really necessary. but if the stand flexes over the years you'll have a problem. better to just shim it now.
regular wood shims will work, but I cut a custom one to fit and stained it to match the stand.

Tanks above 55 gal I recommend to ALWAYS shim and make sure its level front to back and side to side. The undistributed force or uneven force on the silicone seals is what cause tanks to bow leading to leakage. I remember a member on here with a 150 that was complaining that his 150 tall blew twice after resealing and surly enough the back of the tank was off by 1/2 inch and both times it blew it was the back seal. Shimmed it and never had a problem.

Cutting shims are quite dangerous as you cant hold onto the shim leading to it being a possible projectile. I just buy these
http://www.lowes.com/pd_3982-57404-...L=?Ns=p_product_qty_sales_dollar|1&facetInfo=

I used 4 packs on my 220 spread out 1.5-2.0 inches from one another just because the concrete under the carpet was so uneven.

You want to fill the tank about 40% let it sit for a couple hours or even a day and then start to shim it level. But note don't break them off yet. After you get it level fill the tank about 80%-100% and then let it sit for a day and then check it with the level again. Chances are is if you're on carpet you'll need to tap the shims in a bit to compensate for the carpet. Hard wood floors isn't much of a problem but make sure your shimming job takes about 2 days just to make sure everything is settled and correct.

Do you have a level? Should be able to tell before hand if your floor is level or not.

Is the floor level to begin with? Oh nevermind. Just saw.

Honestly I dont know haha! All my tanks are in a den which I personally laid the concrete, I thought it was level but seems like it wasn't. Basically all my tanks are on 70% shims and 30% concrete just because it has high spots. I guess I should have been more careful when laying the concrete lol.

But I would start there. Depending on how much it needs to be adjusted you might have to shim the other side as well to maintain the level. But just start where its logical and keep shimming until the tank is all level making sure you check it with the level often. If you mess up you can just get a pry-bar and stick it under the tank and remove the shims and retry so don't worry about screwing it up lol. I found that I add shims every two inches all around if they fit just for a stronger foundation, but as long as all 4 corners are "planted" its fine.