I'm pretty sure the OP is using the slang term "cinder blocks" but is actually referring to modern concrete blocks. Cinder blocks haven't been manufactured for something like 70 years.
I'm no engineer, but when I built my first "big" tank of 360 gallons I was worried enough to ask one about the strength of both the concrete blocks I hoped to use as a stand, and also the poured concrete high-rise in which my condo was located. He chuckled and showed me some quick numbers. Long story short: despite living directly beneath my unit, a few floors down, he had no concerns about the building.
Regarding the blocks, I showed him my plan for 8 stacked columns of concrete blocks to support the tank, which was going to weigh over 2.5 tons all together. I remember my dismay when he stated they would support a bit less than 1 ton...until he concluded the sentence with the words "per square inch".
Even with the blocks stacked the "wrong" way, i.e. with the holes facing horizontally rather than vertically, the safety factor of that construction was insanely high, somewhere up in the three-digit range. He certainly considered them load-bearing.
Having said that...blocks are heavy and bulky. I would just build a simple stand out of 2x4's; plenty strong enough, fast and easy to build in a couple hours, lightweight and easy to handle, tons of storage space underneath for sumps, equipment, etc.