Fish all look sickly, yet water seems fine...HELP!
 

Just started 2 days ago in my SPS/LPS 150 gallon tank. Have 16 fish, and none look good though they have improved marginally over the past 12 hours. Still cannot see 3 of my 4 tangs at all. I do have 4 mini maxi carpet anemones and they appear to be standing up. Is this a possible cause? Are they possibly mating or are they defending themselves? I did spot a bristle worm recently too. Anyway, any thoughts on this?

It would probably be good to give some background on your system. Size, how long's it been running,, actual test readings, any recent changes or additions, what you've done so far (e.g.. water changes, gfo, carbon etc.)
All those things might help pinpoint a cause.

Is 150 gallon....with 30 gallon sump and skimmer underneath
 

Has been running about 3 years, and give 20 gallon water changes weekly. Have not been home so another person has been caring for it, but says salt is fine and Nitrate is 0.1. But this morning, she says there is a "bad ocean fish smell".

Check your skimmer and empty it
Check arround for leaks

How long has this person been looking after the tank? Is there a possibility she's been topping up with salt water instead of fresh? Obviously diagnosing this will be more difficult if the person on hand hasn't much knowledge on testing, proper water parameters etc. Is there anyone else (a reefer) you know in Okotoks that can pop by and check?

She has been there almost a year as she is renting my house.
 

And things have been good as I have made regular checks to ensure all is well. I wonder if a tang or two has died and is in the live rock somewhere. I am headed out this eve, but wantied to get some thoughts.

2 days and a dead fish should be gone if you got a CUC. Sometime I just toss in a silverside for them to munch on....

Mines a 55g Main & 10g sump

maybe one fish died and caused ammonia, and that can burn the remaining fish or create a lack of oxygen. 16 fish in 150 gallons is a lot, unless they are all small fish. It's 5 gallons of water per 1'' of fish, so that's 30'' of fish, devided by 16, all your fish would need to be like 1.8'' and I am guessing they are much larger then this....

Just overstocked I guess. I don't know the size of your sump but that still make it a lot of fish. Even in 200 gallons your fish would need to be 2.5'' each.

yes...just found a dead tang floating that was in the rock
 

I think that may explain the sickly looking fish.

Well, the first question should be what killed the tang? I'm sure a rotting fish in the water didn't help if it was a decently sized animal, but fish don't just die for no reason. Unless you've had this tank for years and years, chances are good it wasn't old age. If something stressed that guy out mortally there's a good chance others are being subjected to the same pressure.