Hopefully someone reading this might have a better idea of what could have happened than i do.

My marine tank is a fish only system and is 125 gallons.

It has been up about 18 months and basically is quite lightly stocked and has been stable.

In there is (or was) a huge tomato clown (my first marine, from my 1st tank...she is about 4), a Lemonpeel angel (slightly younger than the clown) a chromis and a mandarin. The last two have been in the tank for 12 months ish and were perfectly happy. The mandarin was a great feeder and ate everything.

Yesterday i was about my usual maintainence, scrape off some of the most offending algae, reposition the odd fallen rock, clean up the pumps.

Usual stuff.

An hour after this i noticed the clown acting wierdly. Then a little while later the angel was lieing at the bottom. The general appearance was of a lack of oxygen in the water, gasping for air, acting "dizzy" and uncoordinated.

There was little i could do other than see what the morning would bring.

Which was the corpse of my mandarin (gutted) and the absence of the lemonpeel. Missing presumed eaten by some lucky tank critter.

The clown and bloody chromis are apparently now fine.

My guess is that i managed to stir or shift a deposit of something nasty, which resulted in the deaths. But what would leave the snails alive, the largest and smallest fish, but take out the two medium fishes?

Anyone have any observations? Guesses?

Your guess sounds about right to me, how gutting

My first thought was; was there something on your hands? Oils/chemicals/soaps etc?

As for which fish died, seems sensible that the two hardiest fish (clown/chromis) would live and the two more delicate (mandarin/angel) would die.

Gutting though. Have you taken the basic water chemistry since it happened or at the time, just out of interest? Seems unlikely, but could have been something that is measurable...

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Carbon dioxide can sit under sand and due to the water being a constant warm temp its unable to rise if you moved sand the carbon would have risen and suffocated the fish.

Marina

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"The hand that rocks the cradle is the hand that rules the world"
Friday's child is loving and giving,

its not CO2 under the substrate, but more likely sulphur dioxide, far more toxic, but not likely in marine tanks if u have live rock

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- 2.1.0 Hermanni Tortoises
- 4500L pond
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I'm going to say something to you that's been said to me by every person I've ever loved: I'm really disappointed in you, you are pathetic and weak, and I don't love you anymore. Get out!

Agreed, on both counts!

I think it can still occur in particularly deep substrates though, and under rocks and things.

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Is this a fish only tank or a fish only with live rock?

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