My daughter & son were playing & somehow accidentally threw a piece of gum in my boyfriend's aquarium. Before I could get it out, it had already fell behind the rocks. I'm afraid to tell him, but I'm also afraid not too! Please help...

My daughter and son were playing and somehow accidentally threw a piece of gum in my boyfriend's aquarium. Before I could get it out, it had already fallen behind the rocks. I'm afraid to tell him, but I'm also afraid to not, too! Please help.