Tank Leaking (Then Suddenly Not)?

[Mr Melt]

Hello all; been a long time since I last posted here! Anyways my problem is all in the title lads; apologies in advance if I posted this onto the wrong board.

Anyways, I just bought a brand new Shrimp Set 30 litre tank a good few days ago (living in Lund, Sweden). Set it all up and cycled the tank fine. However a day or two ago I added my 1st fish, and when I floated the bag the water rose right up to the absolute brim (again I figured nothing was amiss). Then all of a sudden I noticed a lot of water around the base of the tank; clearing it revealed more.

Naturally I suspected a leak, and drained it to half tank, which stopped said water from coming out. I should note that the thing wasn't LEAKING, but water seemed to flow out at a rapid pace once I lifted the tank up.
 
Anyways, this morning I removed everything and inspected the base. The glass appeared fine, but there was a cardboard thing on the base that was absolutely drenched. I removed that and rubbed at the seams to remove the last bits of cardboard.

Now as I sit here and type I have drained the tank and removed everything; however I just stress tested the seams with a small bit of water (about 10% total tank volume) and there was no leak. Then again I tested at both 50% and 90% full volume with absolutely no signs of leaking anywhere.

What gives? Could it have been water run off, or something more serious?

Thanks for your time.

PS - I should note that when it appeared to "leak", the water only flowed from the corners where the small "feet" are located (they are clipped on, not built in).

Picture related; store model of the tank I have.

 

 

[Wildbetta]

Did you notice any water leak down from the rim when you floated the bags of fish?  My thoughts would be that the water came out that way and then pooled in the feet and under the tank until you removed it all by cleaning up under the tank.  I would keep an eye on it though to make sure.

 

[iceloly15]

Maybe all the water was too heavy for the tank to carry while less water wasn't? If it continues take it back to the shop to get it checked to ask for a refund if it's truly broken

 

[windsor-aquatic]

The fact that the "leak" stopped when you lowered the water level suggets to me that it could be a seam that's leaking, and lowering the water level relieved the water pressure on the seam, thus closing the seam up again.