It sounds to me like you either have high levels of ammonia or nitrites or both. I realize it may be tempting to just bring your water samples to your LFS
and just have them give you a nod that all is "fine", but what you have to remember is that they are a business. Some LFS
will sell you anything you want and tell you what you want to hear to make the sale. Think of them like used car dealers, there are some good ones out there, but quite a few will try to shove you into something that your not ready for just to make a buck.
I have drafted a few rules that I have found to be prudent to every beginner aquarium hobbyist. They should help you when starting up.
#1. Do your own tests with liquid test kits (API or Sailefert). The only person you should be trusting to test your water is you. After all, its your money thats going to be swimming in it, so it's always better if you know for sure that the water is fine.
#2. Never trust a LFS
right away. When choosing a LFS
, go in and look in their tanks. If you see any fish belly up, gasping, or otherwise in distress, that should be an indicator of the quality of the livestock. It may be a rare case however, so to be sure, tell the clerk about the fish and watch their reaction. If they don't act like they care or act like its the "norm" then its definitely not a good place for you. If they actually seem sincere and try to figure out whats wrong then there may be hope.
#3 When purchasing a fish, research about them to find out if they are really what you want and that you can support it. It helps to have a plan when getting livestock so you know what you want and see if it can work out by comparing to compatibility charts. Again, this goes with #2, the LFS
may try to sell you something that you shouldn't have because of tank size.It may be enticing to get that awesome 10 inch Emperor Angel, but if you have a 20 gal
tank, it's not gonna work.
#4 Research, more research, more patience, more research. SW
tanks take a long time to mature and become stable aquatic ecosystems. Take it slow and before you do something, research the action and decide if its the right course of action to take for you. If you don't know, well that's what were all here for lol.
I hope this little rule sets helps you out a bit and can stop you from having any further losses, they can get expensive after a while.