I had a 13" piece of scrap 2x6 I used to space inside posts. Since its s perfect fit, I cut them so its theyre 1.5x3" blocks attached them half up the inside posts with wood glue, and eyeballed pocket holes in each join. wont add much. but still adds some some extra twist support.
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Don't be floored, the sub $500 stands fail from the slightest thing going wrong.
Case and point, my cat peed on an MDF 10g standI got from petsmart. The stand soaked up pee before I noticed and cleaned it (4 hours max). The next day that edge felt squishy, within a week a 5" section had crumbled leaving just the veneer and a pile of wet sawdust.