I think I may have found what was going on with fishgirls fish, and apparently a few other peoples as well.
The problem seemed to coincide with a new filter (cannister, where as we had used over the back only before) and some work done on the water system. Those two factors, combined with some knowledge from my diving certification classes, lead me to believe that the problem is most likely Gas Bubble Disease. Essentially, GBD is caused when supersaturated gases in the water escape from the water into the body fluids of the fish. Gasses in supersaturated water will try escape out of the water into any medium where the gas saturation level is lower (e.g. into the air, or in the case of gas bubble disease, into the blood and other fluids of the fish). Most commonly seen in the yolk sacs, gills and eyes (and occasionally the fins) as these are the areas of the body which have the most gas permeable membranes. The gas then causes bubbles to form inside capillaries and under the skin, restricting the blood flow and forming hemorrhages and clots.
A quick google will find you tons of advice on the subject, but the basics I've found are:
Reduce algae/plants
Smaller water changes
Agitate the water before adding to the tank
Keep tank temp and added water temp the same
Aerate the tank (helps de-gas)
Make sure your filtration system is not pulling in air, say from a leak, and adding it to the water. Canisters will do this sometimes. I think this may have caused some of our problems.
Here are a couple good links:
http://www.reefs.org/library/article...ki_phipps.html
http://www.thekrib.com/Diseases/gas-bubble.html
http://petplace.compuserve.com/Artic....asp?artID=370
http://www.seahorse.com/articledetail.asp?offset=-1&ArtNo=12
