I had a couple of sand sifters in a 75, pretty much forgot about them. Later, I had an incredible overabundance of bristle worms. Not dozens, but hundreds. Everyone on RC said I MUST be overfeeding, or the bristle worms would not be there. But I fed very sparingly - it was only a quarantine tank with one or two small fish.
Eventually, the worm population became ridiculous - the bottom of the tank was carpeted with bristle worms. But before I could begin siphoning them out, the worms died en mass and crashed the tank.
I figured it out eventually.
I believe the forgotten sand sifters died, perhaps one at a time, and provided food for the worms. When the stars were gone, so was the food source. The worms died, polluted the water, and crashed the tank.
It's the only tank crash I've ever had in 50 years of this hobby.