This is my first aquarium. I have a 5 gal tank with a heater, filter, air stone, plants, gravel and decorations (for hiding). I bought 4 guppies and placed them in the tank Saturday. Went to work this morning and had all 4. Came home and found one on the floor dead (the smallest one). I have a lid so in order for him to have escaped he would've had to leap perfectly in the small space between the lid and side less than 1/4". I cycled the tank prior to stocking the fish. Reading the water every day and get a steady reading of 0.25ppm ammonia, 0 nitrite and 5-10 nitrate. I know guppies jump but the other guppies are much more active than the one who committed suicide. So my question is why did the guppy leap to his death? All 4 guppies were male, no females. Thanks!