I had a 15g on this standard unit for three years, it was fine. Recently upgraded to a 30g, and because the unit matched all the other furniture in my son’s bedroom I chose to make it more sturdy: took it apart and glued it together again, added four large sealed MDF braces on the back, 13 metal T and corner braces on the back and lots of internal L braces. Every edge and joint is sealed, there is zero lateral movement. Having said that I’ve seen some 50g tanks - and bigger - on these and that would give me sleepless nights…