Red and white bristle worms

Question
We have had a healthy saltwater aquarium for about 5 years and suddenly one evening a notice a white worm wiggling up the glass. We looked it up and it was a bristle worm and read it was harmless. So we did nothing. The next morning the water was very cloudy and everything in the aquarium was dead or dying quite shocking to say the least. We decided to break the aquarium down and there  were hundreds of red and white worms in the sand/gravel maybe thousands. Can you think of any reason  why this happened? We figured the worms  were introduce via frozen food as we have not added anything new to the aquarium in well over a year. Would love your input.
Regards ,
Kathy Gordon

Answer
Hello Kathy,

you are correct, bristle worms are not harmful they are actually quite beneficial. the worms had nothing to do with the cloudy water, that could have been many other things including excessive die-off from live rock or if a fish or coral died. the worms in the sand are also beneficial, they are simply hitchhikers from live sand and live rock. nothing was introduced through the frozen food, no need to worry.

hope that helps!

Marcus.