Strange fish loss.

[dkclend]

In the past few weeks I have lost three barnacle blennies and a Mandarin goby. I have no idea why. All other fish are doing well. It is a forty gallon display containing forty lbs of live rock, one clown fish, one cardinal, one yellow head jawfish, two urchins, two lps, and a cuc. All water parameters are fine and tested every other day. Help please.