I have a red eared slider in a outdoor pond which contains approximately 125 gallons of water. I have sand at the bottom of the pond. When I skimmed a net in the sand I pulled up small green brownish bugs that look somewhat like a spider or water crab. There are hundreds of these bugs in the sand. Are they healthy for my turtle? Should I remove the sand and get rid of these bugs? The pond pumps 340 gallon per hour. The water gets pump through a uv light.