Help.... fish leaving this world

[MATRIXINC]

I have had a stable tank for 6+ months. Lately fish have started dieing. There is no obvious disease showing. I test for Nitrite, pH, Specific Gravity, Ammonia. All are good (pH is a bit high). I use only RO water. I change water regularly (every two weeks 20-25%.
I have a shrimp, a choc chip star fish, a larger star fish, and a hermit crab and a few clowns, a yellow tang, angel, a couple of striped damsels, a blue dam.
With in the last few weeks I have lost 2 Monk Idols, 1 anemone, one hermit crab, ...all these loses are from fish/inverts that were doing well for an extended period (not new to the tank).
Water is clear and clean to the eye.
My thoughts is/are 1. two many passive feeders (crab, star fish, anemone, shrimp etc) and there is not enough food left over for them.
Star fish was seen on top of anemone feeding on him...we do not know if this happened post or pre death.
Could the star be eating things like the crab and the Anemone?
Or is this just the natural course of events in a salt water tank?

[Icebox]

Interesting.... I wish I could help more, but here is a bump..

[Maxx]

I test for Nitrite, pH, Specific Gravity, Ammonia. All are good (pH is a bit high).

What are your parameters?

I have lost 2 Monk Idols,

What is a Monk Idol???? Do you mean Moorish Idol?

1 anemone

What kind of anemone? Anemones are difficult to keep at best, and generally not something reccomended for beginners. What kind of lighting do you have? Can you give us more particulars on your system....skimmer/filtration/water flow rates etc.....
Your system might not have been capable of sustaining an anemone.

all these loses are from fish/inverts that were doing well for an extended period (not new to the tank).

Its possible that these could have been caused by a slow malnutrition or wasting away.....
Or your theory on predatory scavengers could be correct as well....
What type of starfish is the larger one?
Nick