tiny animals and worm on my aquarium

Question
Ok, i've have a ten gallon tank and right now it only has one anemone, it had
3 fish and 2 anemones but one died spreading bacteria to the fish and they
eventually died... so now it only one anemone. I have problems keeping the
nitrate to its accurate level because i dont really know how to change the
water and stuff because i asked this guy on a pet store and he said you
should never change the water you should just add more water when it
evaporates, but i really didnt think it was like true... so now i recently
discovered a lot of tiny animals (shrimp like) on the walls of the tank and ill
tell you theyre MILLIONS they reproduce like crazy.. so i started looking on
one of the rocks and i found this NASTY worm... and i dont what to do or if its
good or how the hell did he get in there!! i just want to control the nitrate so
i can have fish again and get rid of the ugly worm. PLEASE HELP ME!

Answer
hi, you should mix up fresh saltwater and do 10% change every week. it sounds to me like you didnt reserch enough into caring for these wild caught sea creatures. the worm is ok so leave well alone, it will help clean your tank as do the copeopods (tiny shrimps)