Applying a soapy sponge to the surface of a fully inflated mattress is the best approach to find a leak. Look out for any spots where bubbles start to appear and grow because that could mean a leak. As an alternative, you can completely inflate the mattress and wait for the sound of air exiting.
Fact
The word “aquarium” means “watering place for cattle” in Latin.
Of course, today’s aquariums aren’t for cows. The first aquarium that looks like what you’d imagine was created in 1921 and opened in 1924 in England.