Those of you who are trying to help me figure out what happened to my clowns - many thanks! I tested my parameters when I saw they were struggling, and here's what I found:
Ammonia - 0 (Red Sea tester)
Nitrite - .05 (previously had been 0 for weeks) (Red Sea)
Nitrate - 8.2 (Hanna)
PH - 8.2 (Red Sea)
Alkalinity - 8.1 (Hanna)
Phosphate - .1 (Salifert)
Salinity 1.025 (Refractometer)
I brought the fish carcasses into the LFS to see if they could diagnose what happened, and also brought my water, which they tested. They also said my parameters were fine, and didn't think the nitrite mini-spike was anything of consequence.
Unfortunately, since the clowns were with me such a short time, I didn't get many pictures of them. The first picture is of them when they were struggling at the surface. You can see the "webbing" on the fin. This fish also had this fin clamped to its side and was not using it. The second picture is of them "well".
For a little background - I decided to start with a QT in August before I had even purchased a DT. I thought that this would help me get used to testing parameters and water keeping. After the QT cycled, I bought a huge arrow crab thinking this would be the first resident of my DT. She's been alone in there since about the end of August. In November, I saw these clowns at my LFS, and they were exactly what I wanted, and since I hadn't seen any for sale since I've started looking at reef fish, I thought I would buy them and put them in my QT. I was however, afraid of the huge arrow crab since the clowns were so small (less than 1"). So I bought a breeder box to keep them in while I waited on a tank divider. They were in the breeder box for maybe 5 days, and then I put them in the QT. They seemed fine while in the breeder box. It was after I put them in the QT that they struggled. I have a HOB filter for the QT, and I moved it over to split the flow between the arrow crab section and the clown section, but I did this after the first 2 days the clowns were in there, so it's possible that they weren't getting enough flow. The divider did have holes in it, so I thought this would be enough for air/water exchange between the 2 sides.
Thanks for any ideas you have about what might have gone wrong. The LFS has graciously said they will replace the clowns once I'm ready for more. I've started a 2nd QT, since now I'm going to have to assume my original QT has some sort of cooties, and will let that one run fallow for 3 months. I'm definitely going to QT any fish or inverts that I buy. That was my plan even before all this happened! Only now, I think rather than just observing them, I'm going to actively treat them, too.