you'd see salt marks around the silicone and stand if there was a leak, mostlikely its evaporating. i have to top up about 1/2" of water every 3 days in my 26gallon. the more surface area, air movement and water movement, along with a higher temps causes water to evaporate at different rates, but you need surface agitation and temps around 76-80 degrees so its really just a matter of topping up or getting cover which non of us would recommend