It does bow to the middle slightly but each self is rated to 800lb. So I hope so. I also skipped a step and did not screw the cement board to the rails
Going to assume the racks were installed correctly however your floor may be severely pitched. Would suggest you take a level to it to find out for certain other wise the shelves may need to be reinforced.
The screws in the shelves hold it stationary and also hasten flex when there is uneven weight distribution. If the shelf start to bow longitudinally in the center, you've done yourself a disservice by not adding the screws as a reinforcement.
It currently looks like it's pitched to the right and forward towards that corner. I hope the floor isn't giving way to the weight on that corner of the rack. For safety, I would recommend placing the entire rack on top of a wooden board to spread the weight of the four corners to the entire surface floor of the shelf.
The last thing you want to have is have an unscheduled tank teardown.