Some eat corals.....
Fish too fast
For years I listened to people who said this/that/ and the other were safe.
Only once did I ever catch one red handed, a red legged hermit, who somehow grabbed one of my real expensive clowns from the bottom of the belly. Then over time, list some snails, sometimes a coral would retract out of the blue, sometimes lose a coral.
Yup, can't prove much, but since my last rebuild, 17 months ago where I banned all except corals, nem, fish and snails....I have yet to lose anything....more than 50 corals, 6 fish, 3 shrimp and 31 snails alive and well...17 months and counting.....Hum!...... Just my view on the unknown things that should be safe.....
This is not to say people are incorrect....there is:
-the things known to attack others and consume, the predators.
-the things that if given the chance, will attack and consume others, the opportunists
-the things that will consume things it doesn't usually because of a lack of food, especially crabs, the survivalist.
-the things that, in most cases, are capable of defending themselves or have the speed to run away.
When we add an enclosed space, all things can change...
