Salt Water Help

[jerwrigh]

I have a 55 Gallon saltwater tank that has been up and running for four years. Over the last year, for whatever reason, I have not been able to add any thing to the tank including fish and starfish. They day within days. I am down to three fish in the tank. I took a sample of the water and had it tested and they said it was perfect. So I am looking for any clues as to what is going on with my tank. The last thing I introduced was a starfish and it died after one day.

Help in GA!!!

 

[lmforbis]

It would help to have actual numbers for your test results and maybe some pics.
amonia
nitrite
nitrate
phosphate
pH
temp
salinity - how measured
calcium
magnesium
alkalinity
I is best if you have your own test kits to test your water
Are you using tap water to make your salt water/top off tank?
Starfish and related animals are very sensitive to changes in water and need to be acclimated slowly or they will die.