SPS dying...oh no!

[Cabo31]

So here's the story. I have had problems the last 2 months with sps dying from the base up(stn). It start on one coral and has now spread to several. We do not see any visible pests, but I did remove 3 gorilla crabs in the past. Here are our current parameters:
Stock-4 clowns and 1 wrasse
Salinity 1.027
Alk (red sea) 9 and (Hanna) 10.1
Calcium 440
Magnesium 1440
Phosphate 0(never had any reading)
Nitrate 1-2

We do water change of 15 gallons once a week.we have a RedSea reefer 250(60 gallon).
The light is an ATI hybrid. The tank is a year old. We have a mixed coral tank. I have notices some bubble alge in the tank,but not tremendous amount. I am not currently running any carbon or GFO. We have lost 5 pieces already!
Any suggestions? What should I do? Look for? Change?

 

[ycnibrc]

check for AEFW take some of the infected coral and dip. If no flat worm then check your flow if not enough flow to your corals the waste produce by your corals doesn't float away therefore easier to get infected and stn. Assume that all parameter are correct.