Dead Amano!

[titusmighty]

I came home from work today to find all my Amano shrimp (about 20) dead.

The only thing that has changed in the past week is the light cycle.

The tank has a pH of 7, 0 ammonia, Nitrate of 10, Nitrite of 0.5

None of the fish are dead or appear in any way strange. There are about 10 tetras, 3 barbs, 4 guppies, 2 bushy nose pleco.

30 gallons, ViaAqua 750 Canister filter, Coralife 9 watt UV sterilizer, CO2.

The tank is heavily planted.

Why would this have happened?

Thank you.

 

[Liam]

The nitrite sounds like the mostly likely cause of death, they are a lot less tolerant of nitrite than fish. Otherwise it may be something in the water like copper, but any nitrite can kill them, when they are in trouble they usually try and get out of the tank, start swimming about madly etc, so one would expect to see that for some hours before they died. The light change wouldnt have bothered them.

 

[A creature void of form]

Liam's answer sounds the most plausible.

But how long have you had them for? They moult their exo-skeletons every 3-4 months and are very vunerable indeed during this time. I'm not sure if the shrimp moult simultaneusly, but if that is the case then the slightest knock from your fish is enough to kill all 20 of them. I've only had mine for a week though, so I'm not sure.

 

[titusmighty]

They weren't displaying at all.

However, I think it was lack of oxygen that killed them.

I noticed the fish all went to the top of the tank this evening, displaying, etc. Since I did a 50% water change yesterday after the shrimp died and know all levels are normal, I'm pretty sure it was oxygen.

I switched to a cannister filter about a month ago. A week ago, I took off the wet/dry filter that was on there - it has an air valve that mixes oxygen with the water to improve gas exchange.

I put the filter back on and the fish are now resuming normal behavior. Tomorrow I'll pick up some air stones and hopefully that will solve the problem.