Setternut, 2 things will always show up in water...Leeches and snails!

Your HBG will eat some leeches and very small snails, but Redear sunfish will give FAR better snail control. Infestations of snails and leeches are unavoidable as they are both easily introduced to your pond on the legs of birds and other critters travelling to different water bodies. The infestations will ebb and flow a lot also....one year can be horrible, and the next year not see a one.