mysterous disease - HELP

[chrisg]

I am ready to give up fish keeping (for the second time in ten years)
I have a fish only . 55g saltwater tank. My goal has been to keep it simple and keep fish alive. I use a wetdry, good protein skimmer, RO water, 25 percent water changes every month, all measurements are fine, (nitrates about 20) vitually no algae. The tank is not overloaded. At its peak, (before the plague) I had six fish. Now the bad part.
In June 2002, I introduced a 4" naso tang. He ate great for a month. One month later, my eight lined wrasse stopped eating and died with two days. There were no external parasites at all. In July, about two weeks after the wrasse died, Naso tang went the same way. I tried QT with antibiotics, with no success. Naso died within a day. LFS said wrasse probably died from old age and Naso from cyanide. OK. Today, my yellow tang (who has been in the tank for a year) died the same way. Again, no external parasites or spots.
I am left with only guesses:
Naso introduced some tough bacterial or viral infection.
The dried seaweed I started using when I got Naso contains a toxin.
I WOULD BE EXTREMELY GRATEFULL FOR ANY THOUGHTS.

 

[beth]

What are your current water readings: ammonia, nitrite, nitrates, phosphates?
Have you added any kind of medication to your tank, and, if so, what?
Were any of these fish "sick" first, or did they just drop dead out of the blue? How did they look in terms of color, body weight, behavior?

 

[chrisg]

Beth,
Thanks for the quick response. Here is some information I hope helps. I retested everything this morning, using a red-sea test kit.
Numbers are as follows:
ph 8.1
temp 80 degrees
Ammonia .20 total (toxic ammonia per the test kit is 6% of that, or .012 ppm) I have no idea why I am getting any reading, or if this reading is a problem.
Nitrites 0
Nitrates 10 ppm.
Phosphate - I don't test for it, but I use RO water for water changes and evaporation. Also, I don't have any algae to speak of, so I am assuming phosphates are not that high.
Fish and dates of introduction:
Blue Damsel 8/01
Tomato Clown 10/01
Eight Lined wrasse 10/01 (died 6/28/02)
Yellow Tang 2/01 (died 9/27/02)
Fiji Puffer 2/01
Naso Tang 06/15/02 (died 7/19/02)
They are fed frozen brine shrimp plus and dry roasted seaweed.
The only medication I have ever used was after the Naso tang died on 7/10/02. It was Aquatronics Discomed (Levamisol, NaCl, Piperazine, Magnesium sulfate, Neomycin). It was introduced to the food for a few days, per advice of LFS.
Fish behavior of all fish has been fine, appearing stress-free. All eat/ate well. No fin tears or wounds.
As for the sick fish: All appeared/behaved fine until suddenly,
Day 1: Hiding, not eating.
Day 2. Hiding, laying on bottom, some loss of balance.
Day 3 Dead.
None displayed any signs of breathing problems. The only changes in color where some discoloration in the form of minor redness and loss of color. This occured at the end, near death.
I don't use a QT before introducing fish. I know I should. However, the Naso tang behaved fine, ate well right away and did fine for four weeks. So, I probably would have moved him into the tank from the QT anyway.
I know this is alot. Thanks.
Chris

 

[chrisg]

Rechecked ammonia again and it is 0 ppm, not 20 ppm. I must have misread earlier test