It might also be the weight limit of the legs of the table, more then the glass.
Don't forget while you're resting your arms on the desk while typing or fish watching, it adds more weight and pressure.
I'd add a support just for giggles, if possible. Do you have pictures of the stand?
One method I've used to determine how strong a table or desk is, is to add weights, in excess of the expected load by about 50lbs, this way if I trip into it, it won't explode..
Or.. it breaks under the load and drops weights on the ground.. which is considerably better then fish, water, time and effort.
EDIT: just clicked the link (didn't show on phone mode) hmm.. that's tough to brace without looking like it's rigged up... You may be reaching it's tolerances, but if I were the company.. I'd also put out a number slightly lower then the actual max capacity..
That's just my opinion though. I'd be cautious.
Lo, they do call to me.
They bid me take my place among them
In the halls of Valhalla
Where the brave may live forever.