[swrzoe]

long sand tubes being built in substrate also white hair size worms extending out of sand . are these harmfull

 

[Imaexpat2]

No these are beneficial critters hat you certianly want in your system. They are detravores and will help keep your tank clean and healthy. I go to great lengths to have as diverse a sand bed fauna as absolutely possible. This is why I do not keep Sand Sifting Stars or sand sifting Gobies in my tanks as they have a tendemcy to deplete such things from the sand beds. Besides thier obvious benefit they are also kind of interesting to watch and observe as they go about thier business in the tank.