sudden fish mortality... please help!

[amandaschlicher]

hey guys. i started a 75 gal fish only tank 3 months ago. i have 1 domino damsel, 2 yellow tail blue damsels, 1 yellow tang, 2 clownfish, 1 coral beauty angel and 3 turbo snails. i have been adding fish slowly and checking parameters, and i had not yet done a water change. i did a test yesterday and got these results: sg 1.021, pH 8.4, ammonia 3ppm, nitrates 40ppm, nitrites .5ppm. yesterday i did a 15 gal water change. all my fish seemed fine at the time. i came back 2 hours later and my coral beauty was lying on its side gasping. today i found it dead. now my yellow tang is doing the same thing. i'm not sure what the new parameters are, since i test my water at a fish store. what's going on? all of this started within an hour or two of changing the water. did i screw something up with the water change?

 

[a&m aggie 04']

ammonia at 3ppm is very high, any ammonia can kill fish, i think your salinity should be a little higher but thats probably not what killed your fish. Nitrites are also very toxic. You really need to invest in a test kit of your own, so you can get reading w/o making a trip to the store. Is anything in your tank missing? Anything dead in your tank can cause ammonia to rise, some corals put off diff. toxins when dead. Do a count on all your inhabitants to see if anything is missing.
Did you use freshly mixed saltwater for your water change, newly made saltwater can be irritating to your fish but im not sure if it can kill them.
You need to get the ammonia down, might have to do a more drastic water change.
mark

 

[jcb101]

agree with above, but do a 10% water change every 3 weeks and do a 25% now and get a decent test kit.

 

[fshhub]

ammonia being that high is definitely a problem, your tank may have either experienced a loss which could result in the ammonia, or maybe has not yet stabilized, they cycle may not have completed before you started adding fish
what are you using for filtration, substrate and rock??
honestly a 3 month old tank should not be stocked nearly that heavily, IMO. i am setting up a tank that we started in feb. that does not have that much in it, and has 90 lbs of lr a 4 inch sand bed and a skimmer, and we did not start adding fish for about 6 weeks, by 3 months, it only had 2 fish in it
and not to sound too forward, but anohter problem i see is the dwarf angel they should only be added to mature systems, which i would not do until after the tank has cycled and been running for at least 6 months with stable conditions, they are very delicate fish that need good stable conditions
my guess is on the fact that the tank never cycled properly before adding fish, and each new addition only throws things out of whack again with it not being stable to start with
sorry but i agree with the others and also see this as a good part of your problem, cycling is not a time thing, but a question of stability or equilllibrium(tanks anthem) and does not finish until after the tank reaches this state and adding new additions before it does, only adds to more potential problems until it actually finishes
one other possibility is over feeding, how often and how much do you feed?