You could probably get away with the 1″ but you’d have to brace the out of it. For an aquarium that big, I’d probably use 2″ or 1.5″ which is the 15 series. I know Parco sells some black t-slot that would look cool for that.
Using T-Slot for Aquarium Is pretty clever as aluminum doesn’t rust and gives a nice look to the aquarium.
But we have to choose the tubing size according to the weight of the aquarium and many high end aquarium come with aluminium stand.