can crash soft coral colonies fast, so can major water fluctuations. The stuff grows like weeds under proper conditions, but can melt in days, polluting your tank and setting off a chain reaction. The coral can emit a chemical that tells the other corals like it that the end is near.
If you mean dirty water in the definition it is loaded with tasty floating food critters, then yes, they can also filter feed. But they want pretty good quality water to survive.