Greetings to all! I need help with my 50 gal. Albino Frog tank. Just discovered lots of small, semi-transparent stingray or horseshoe crab like creatures in 50 gal. tank. They swim very fast and frequently rest throughout the gravel. Range in size so looks as though they are hatching at different stages. Have had frogs for 2-3 years and never noticed this before. Did do a complete water change 2 weeks ago. Any ideas on what they are and how do I get rid of them, and thirdly, have noticed the frogs scarfing on a few. Is that bad? Thanks in advance for you help!