Recently added a diamond goby that jumped out (and died) within a few days.
Also tried adding a diamond goby a month ago that also jumped out (and died).
We have plastic egg crates over the tank, but they both appeared to have jumped out while we removed them to do water changes... both seemed to do it either while we were pouring in the water (and was not noticed) or the brief minute or two while transferring water from the tank to the sink. We don't buy any more diamond goby's.
I don't think the tank is overstocked. We have 1 wrass. 2 green chromis damsels. 1 clownfish. And the yellow tang. We also have about 10-12 hermit crabs and about 4 or 5 turbo snails. A couple nacarius (sp?) snails and 2 cleaner shrimp.
We had a flame angel that lasted about 6-9 months before vanishing (we believe it died and got eaten by the cleaning crew).
The fish seem lively, and we do weekly PCW's (15%-20%).
We recently had a bloom of green hair algae, and are trying to aggressively treat it. Nitrates are at 25ppm... maybe 30ppm. The best we were able to have them was around 10-15ppm. The old drop testers showed apx. ZERO ppm
... but I since purchased newer testers that haven't expired and they seem much more accurate.