parasites??

Question
i have a marine tank which has been running for several years. i have live rock which has been in the tank for many years. I have live green plants in my tank which grew out of the live rock also. recently i have many tiny red worms which look like tiny centepedes, and tiny grey shrimp like creatures running thru out the bottom of the tank. They dont seem to be causing any harm, in fact they help keep the bottom and rocks clean.  Do you know what these 2 creatures are?? willl they harm my fish?

Answer
Hi Terri. It sounds to me like you have a good supply of bristleworms and Gammaridean amphipods in your tank. This is a good sign that the tank is healthy and these two creatures are very beneficial to your system. They will not harm your fish. They are scavengers and can, in some cases, be food for your fish!