It is a shame some are pretty like this one shown. I am lucky I never have had any of them.....A friend with a 75 had little yellow ones get out of control on a couple rocks in the back of her tank.......
After weeks of trying to rid them, using Kalk paste, lemon juice, etc. She eventually gave up and removed those rocks to disinfect them.. ...... They easily can become insidious little killing pest.......