Hello; I know that concrete blocks are not safe to use to hold up a car, but your 180 will weigh between 1800 and 2160 pounds which is less than most cars. you also plan to use several stacks so the weight will be spread over more than four points. As for as suggestions, three came to mind.
First is that boards or a sheet of plywood be placed on top of the cement blocks and under the tank. (Some have also posted of having a layer of dense foam under a tank, I believe this is to help keep any potential high spots from cracking the tank.) (Perhaps someone who has done this will post about it?)
Another is to place the cement blocks in their strongest orientation. I believe this is the way they would go if a part of a wall, which is with the holes facing up??
Last is that the cement block stand be as level a possible with all the stacks as close to the same height as possible.
I have not used cement blocks as a stand for a tank as big as you have, so do not know what the actual problems may turn out to be. Let us hope someone with actual experience will post.