How to find a leak?

So I've ran into a minor emergency... Setting up a 29 gallon for my sons room, already got the 3D background siliconed in and thought to myself "self, I'd better leak test this used tank"... Set it on my kitchen table, filled it, no problem for 2 days... woke up today to water on the table...

It appears to be leaking on the bottom somewhere, but with the black tank trim, I'm not sure where... All the corners are good top to bottom, no moisture there...

Problem is, since the background is already in place, I'm not sure I can save it, or I'd just go grab another tank and do it all over again... Or I could bust/pry the tank apart to get it out...

Other problem is I was hoping to get it setup and at least water running/filtering by Sunday when we have his party, so he could at least see something up and going now (6 year olds aren't good with delayed gratification).

Any way to find the leak easy? Or should I just strip and re-caulk the three inside bottom edges I can get to and hope for the best?

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That's what I was afraid of, I did one seam because it was mostly gone, so I stripped that whole inside corner and re-did it.

I've got two 29 tanks, and I think this one had been used for lizards (so it was probably a bad idea from the start) but on the other 29, the trim ring around the top is cracked in the middle front and back, and one corner is cracked... so I didn't want to chance it either...

Might just go out this weekend and see if I can find a bow front to fit on his dresser...

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