How to Find and Kill Evil Hitchhikers

[Canadbis]

Did something maybe come in on the GSP or other frags you have just introduced?
Maybe you added to much at once?

[Pier Pressure]

Okay just did further research on the brittle star as well as further research on the sea apples.

The only brittle star I could find that is "rumoured" to have eaten fish is a green one, and this thing is definitely purple. Plus fish bodies were not eaten or ravaged, so if the brittle star was preying on the fish I think their little bodies should have shown more evidence of same. The only thing we noticed on the dead fish was that their gills were a bit puffy.

The sea apples are one of the first thing that I put into the aquarium and they can be seen feeding daily - that is, one feeder tentacle after another is placed in their mouths, they are breathing out of their butts fine (cool feature, eh?) and they do not appear stressed at all. Their positioning within the tank did not change at all on the night of death in question.

I am going to try that bottle thingy tonight. If I come up with anything weird, or anything changes, I shall of course update this thread.

Canabis, that is exactly what I am thinking.

Karen

[dunl]

If the only sign of damage was puffy gills, I say it's not an animal. I know of no animal that kills others leaving puffy gills as the only evidence.

[mark]

Your test kits current, checking for the usual (NH3, Nitrates), salinity, no stray currents, no temp swings?

Checking the tank in the middle of the night with a red lensed light?

[Ruth]

With that many fish etc. dieing in that short of period of time I highly doubt that it is a predator hitchiker. Particularly since you say they had no other marks on them other than puffy gills.
A couple of possibilities come to my pea brain. Did you by any chance have a power outage or loose circulation for a period of time? Do you run a skimmer and perhaps shut it off overnight. The reason I ask is because when I had a breaker trip and lost circulation overnight in one of my tanks I lost 4 fish (out of 7) and it was from lack of oxygen in the water. For the most part the fish I lost were large however on very large one (my Naso Tang)survived. Some fish are way more suseptable to an oxygen drop.
The next thing to explore is water quality. I know you tested yours but could you please let us know what brand of test kit you are using and what your #'s for Ammonia, Nitrate, Nitrite, PH, calcium, alk/dkh, and magnesium are. Sometimes it can be an inbalance in chemestry however I do not suspect this in your case.
Of course the last thing is some kind of disease that only effected some of your livestock and that list is way too long and complicated to try and guess at.

[Okguy]

I normally just lurk in the background around here, but I thought I would put my 2 cents in on this one. I agree with Ruth.

Originally Posted by Ruth

With that many fish etc. dieing in that short of period of time I highly doubt that it is a predator hitchiker. Particularly since you say they had no other marks on them other than puffy gills.
A couple of possibilities come to my pea brain. Did you by any chance have a power outage or loose circulation for a period of time? Do you run a skimmer and perhaps shut it off overnight. The reason I ask is because when I had a breaker trip and lost circulation overnight in one of my tanks I lost 4 fish (out of 7) and it was from lack of oxygen in the water. Some fish are way more suseptable to an oxygen drop.

Clearly not enough carnage to be a killer hitchhiker. Believe me I've seen my fair share of them...

My feeling is that the bioload was just too high to maintain the oxygen level at night or the CO2 levels got too high. 6 fish in a 28 gallon is an extremely high. While you're able to maintain the water quality with weekly water changes the oxygen levels we're probably dangerously low at night as everything in the tank would be using the oxygen and nothing can be creating it (unless you have a refugium on a reverse photo period). Adding the new critters probably put you over the top. In an oxygen deprived enviroment the larger more advanced species usually go first (ie. the fish and the shrimp). Which would explain why the hermits, snails and corals survived. The firefish just got lucky and it would explain why he is now freaked out. I think I would be freaked out if I almost suffocated .

Good Luck!

Kevin