[Allanira]

Well here is a sad story atleast for me. 3 days ago when I was feeding my sw tank my Coris Wrasse went into hiding. I checked the water params and they were fine. He/she was still hiding the next day. It came out for a couple mins before feeding time then went into hiding again. Well yesterday morning I found it dead in the far back right corner of my tank. I fished it out as soon as I saw it and checked my water params again. I had a small ammonia spike so I have water getting ready for another water change. I just did a water change earlier this week also. I am using the same salt and the same water as usual. I dont know what happened to it. What should I be looking for in my other fish? Could it be something that can pass from it to the other 3 that I have? Should I be worried about my other fish just dying like that? I need some info for this so I know what to look for. The Wrasse was eating great right before this. It was being a little piggy about food. My other 3 are still eating fine but I am now worried about what could go wrong with them. My water params before the Wrasse died were
S.G. 1.024
pH 8.4
Alk 2.9
Ammonia 0ppm
Nitrite 0ppm
Nitrate 20ppm
Cal 490
Thats all the tests I have. I keep the lights off a lot of the time right now cause of the wrasse dying. Should I turn them back on? They are on for abuot 9hrs a day right now. They were on for 12hors. Please I need answers. This is the first fish that I have had die on me (not counting the green chromis that committed suicide) . Thank you in advance for an advise you give me. Also I forgot to say that there were no marks on the body.