I have a 55 gallon freshwater tropical community tank. I was recently performing a deep clean and on one of my lava rocks I saw two of these little creatures. They were blueish in color and have legs. They didn’t exactly seem like shrimp, but I’m not sure. They weren’t moving at first so I poked them and they scurried around pretty fast, considering their size. They were tiny; maybe about 1cm fully extended.