Four of your brackets are taking all of the load. The outer brackets are only holding the rods in place. What you've created is a simple lever on the inner brackets and you're actually multiplying the forces there. You've got straight line force on wood fibers. Start sloshing water around added to your actually moving the tank and you're just asking for trouble. We're only trying to help you avoid a problem. Trust me, I've built a few things that sounded good, worked in theory, and actually worked great in practice. For a while. Fortunately those instances have been rare. Sort of. Last one was a lumber cart. Looked great though
I forgot about the multiplying forces!
My dad had convinced me that the screws would hold, but I don't think he did the math
I'm going to have to talk to him about it again... I have a couple of ideas for strengthening it, so I guess stay tuned!