[quote]should i mortar the bricks/ cement blocks together before putting on the 2x4's?[/quote]No. The weight of the aquarium holds the setup together.
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Also, although I love Kenshin_Himura, none of the leveling/shimming/etc. that he suggests is necessary, unless the floor you're putting the tank on is not level. Just stack the blocks, place the 2X4s on the blocks, put the empty aquarium on the 2X4s, double check that [b]the entire outer edge of the aquarium is on the wood[/b], and fill it with water. The weight of the tank settles itself "into" the wood. Supporting the glass on the bottom of the tank is unnecessary.
I've seen about a dozen LFSs (local yocals) simply build 2X4 frames and put huge aquariums in them, which is where I got the idea. I've stacked blocks/2X4s/aquariums on at least five 55+ tanks that I can remember and have left them for years without any problem whatsoever. Within the next few days I'll take some pix of my current setup and try to post them so you can see. Bonnie (my better half) made a blue skirting around my current tank that makes it look cool. --Mark