Fish death

Question
QUESTION: Hi, it's me again.... I have never been more confused than I am right now. I went back to the pet store earlier today to buy a new damsel. I was talking with the guys at the pet store and they claim that damsels were nearly impossible to kill and something would have to be royally messed up for them to die (keep in mind both of my damsels had died within the past two days). So I bought another damsel today because I figured that my tank was stable again (Also because my clown fish is perfectly fine as well). I put the damsel in when I got home (obviously letting the bag sit in the tank for 15 mins to balance the temperature) it seemed completely fine for the next 2 hours. I left to go to school and when I got back, it was lying on the bottom of the tank dead. I have never been more confused. My clown fish is perfectly fine, yet these so-called 'invincible' fish keep dying on me. Something must have gone wrong, and I am clearly not seeing it. Do you have any idea what could have happened?
Thanks

ANSWER: Mitch,

Yes I have ideas.  Damsels are indeed very hearty and I'm very surprised the clown is alive if the damsel is not.

Sometimes, damsels come sick.  Was it in great shape?  Did you thoroughly check it?

Take your water to the petstore and have it tested ASAP, it is urgent.  If something is awry, then you need to get it under control, before the clownfish dies too.

Please make sure you are using dechlorinator when you add water if it's not R/O water.  Be sure you test the amount of salt in the water.  That is utmost important!  It should ideally be 1.024.

Please send me your water test results.  Meantime, check salinity.  Check filtration.  Check dechlorination...

Write back and I'll help you figure this out.

---------- FOLLOW-UP ----------

QUESTION: As far as I know the fish was in good condition. the only thing I noticed was that there was a spot on its nose (this is a blue damsel btw). the other blue damsel that i had didnt have this spot. I assumed that it was natural and I didn't think anything of it. Other than that, the fish behavior seemed fine, there were no frayed fins or anything, so I don't think it was sick (but then again, I am fairly new at this and it would be hard for me to spot out a defect if I've never seen one before) I only used the R/O water. I didn't use any tap water at all. The salinity is barley below 1.024. I added a new filter cartridge today (I don't know if that is significant or not). Temperature is at about 74. I will get a water test done as soon as I can and then I will send you the results.
Thanks!!!

ANSWER: The temp is too low.  You want to be up near 76.  74 is not great.  Thanks and let me know what's going on with the results.  It could be a ph issue.

---------- FOLLOW-UP ----------

QUESTION: Hello
I got the water tested today. The ammonia is at a 0.25. The nitrates and nitrites are both below 20. The PH is at 8.0. The salinity is at 1.024. I bought some PH buffer which is supposed to bring the PH back to about 8.3. Once again, other than the PH, everything seemed okay. I also noticed that my Gorgonian has started to lose skin. I don't think that is normal. The clown fish seems to be okay although it generally stays on one side of the tank and almost never goes on to the other (I know that they are very territorial, so I don't know if that has anything to do with it or not). I asked the pet store what they thought about the damsel that died, and he said he also had no idea but it could simply be that the damsel I got wasn't healthy (which made me a little aggravated because he was the one who picked it out for me). If that is the case then I will be sure to pick the next one myself.

Answer
Hi Mitch,

Ammonia has to be 0, and 25 is off the charts for a reef tank.  That can be compensated by using zeolyte crystals for a few days in the sump.  Put them into a net.  Let the sump flow over them.

Nitrites have to be 0.  Again, anything on nitrates is off the charts for a reef tank.

The Nitrates can't be higher than 10.  That means everything is exhibiting water quality issues, as suspected.

You need to change 25% of the water today.  You need to change 10% of the water every other day for a week after that. Your water quality is very poor.

The PH isn't any issue compared to the ammonia, nitrates and nitrites.  They are way too high.

Whatever method of filtration is being used, it is not sufficient.  I would try to revamp this, add a skimmer and do more frequent water changes.  Water has to be changed in a salt tank every 2 weeks, at the least.  I do mine weekly, and it runs okay.

Mitch, your fish will keep dying as long as the nitrates, nitrites and ammonia are this high. :(  I'm so sad for you.  It's really frustrating, I know.  

Keep in touch all you need and I'll help you all I can.