...Important to stack blocks with the hole up as used for walls...
Not really. While it's true that aligning the blocks with the gaps vertical ensures the absolute maximum strength, it also makes for the absolute worst waste of space. From a practical standpoint, stacking the blocks with the gaps horizontal provides a number of small cubbyholes which can be useful for storage and for routing of hoses, airlines, wiring, etc.; the strength of the blocks is still so immense that it far exceeds anything you will need for mere aquarium use.
The structural engineer I mentioned earlier was adamant that a single block, or a single stack of them, would be more than capable of supporting the entire weight of the tank I was building entirely on its own...although of course the tank would have torn itself apart of its own weight if balanced on such a tiny support. For the OP, top the columns of concrete blocks with wood to support the bottom of the tank evenly; but orient the blocks any which way you want, it will never make any practical difference in terms of strength.