Lionfish not eating and lying on bottom

[jzlahmar]

I have a Volitan Lionfish. I have had him since April of 2010. He has always been active and lively in my 180 gallon tank. I have not added any new tank mates recently. Currently, the co-habitants are: Niger Trigger, Clown Trigger, Snowflake Eel, Queen Angel, Sigapore Angel, Yellow Tang, Convict Tang, 3 Damsels, Porcupine Puffer, Tomato Clown.
The usual diet of my Lionfish is frozen krill. He has been eating this since day one and I usually feed him every other day. I fed the Lionfish scallops about 1.5 weeks ago. Since then, he has not eaten and has been hanging out in a cave. He lies on the bottom of the cave, not moving and lifeless. His fins are drooping and he has not left the cave in a week and a half. I am very upset because he was one of my first fish and I am so attached to him.
I have checked all parameters in the tank. The nitrate level is between 5 and 10. The pH is 7.8. The ammonia is 0. The temperature is about 81 degrees. I know the temperature is a bit high but with 4 submersible pumps. I do a 40 percent water change every 3 weeks. I heard buying Rosey Red Minnows or Ghost Shrimp might temp him. Is this true? Should I quarantine him? What can I do to save him?

[Cronamator]

i moved the topic here to get some emergency exposure.

QT is always recommended. however, sometimes it can do more harm than good when they are stressed. if it isnt showing any visible signs of disease i would leave it. as far as your water perameters go, your Ph is a little low. try to raise it slowly to about 8.1-8.3(ideal) what time of the day are you testing it? if your testing just after lights on or the lights are off, that number is about normal as Ph lowers during those times.

[J-P]

what are the tank stats?
ammonia,
nitrite
nitrate

"The usual diet of my Lionfish is frozen krill. He has been eating this since day one and I usually feed him every other day. I fed the Lionfish scallops about 1.5 weeks ago. Since then, he has not eaten and has been hanging out in a cave."

A varied diet it is crucial. Is it possible he has constipation? A week and a half is a long time to go... Were the scallops raw or pre cooked?

[jzlahmar]

Hi all. Thank you for all your responses. I took my lionfish back to the lfs. I asked them to take him in because their water is immaculate and there is a bit of copper in case of disease. He still isn't looking too well though.
I tested my water. The nitrates are between 5 and 10. They ammonia is 0. I bought a pH buffer and have been adding this to the tank over the past couple days.
Is lionfish suppose to be a hardy fish?

[jzlahmar]

The scallops were raw and I froze them.

[J-P]

I have never kept one, but I keep reading about them because I want one

They are fairly delicate fish, more pertaining to the diet than water perams from what I have read. Vitamin deficiencies are usually the culprits. BUT again this is not first hand experience, just what I was researching before buying one.