Mass Loss Of Fish

[MHunt]

But dropsy is a symptom of something else, not a cause. Very odd.

 

[InaneCathode]

but my nitrates where high - probably the cause I think

mate... it WAS NOT your nitrate

it was the ammonia and nitrite. both are highly toxic.


there is something very wrong if a tank established for a year or more has ammonia and nitrite readings of any sort

what sort of filter did you have?
how were you cleaning it?
did you perform any sort fo change to the tank in the days leading up to the wipeout?

any time you test your water and see an ammonia or nitrite reading with livestock in the tank it means you are either way over feeding, your filter is not sufficient for the job or both

sorry miss spelling by me on that one!

I did have an old fluval filter, I cleaned it by using some old tank water in a bowl. I did a change about 4 days before the loss (i think)

Bam! Thats what killed your tank dude. The fact that you changed your filter wouldnt matter much, but that in combination with you putting a feeder block (pause for a second, feeder blocks are notorious for ammonia bombing tanks, the release method isnt very well controlled and more often than not they end up dumping a ton of food into the tank which then rots into ammonia and other nasties) into your tank effectively sterilized your tank with ammonia.

When you change out a filter for a brand new (stirile) one your biological filter goes with the old one, into the trash. So now you have a filter that has no capacity for processing ammonia, perhaps that alone would cause a few fish deaths and maybe a moderate ammonia spike. But then, when you put the feeder block in there, it dissolved way too quickly and dumped a ton of unused food into the tank, rotting, and turning into ammonia. This turned what could have been a reletively minor event into a whole tank death.

Changing filters: Shouldnt have to be done unless they're super clogged. In which case run another filter next to it for a few weeks, then use that filter (cultivate a new filter bed basically)
Feeding blocks: Never. Fish are cold blooded, and can go a week without eating no problem (unless they're really tiny fish, fry for example)

EDIT: Ammonia events seem sudden sometimes in compared with how slowing things tend to happen in the tank. One day they're fine, the next day they're either gasping like crazy or dead.

 

[Tolak]

Feeder blocks=pollution. Many aquatics products are sold that do nothing good nor bad for the fish, but make the aquarist feel better. Products with aloe, many bacterial starter products, a whole lot of others do nothing good, but nothing bad either. Those feeder blocks are one of the few products that actually do something bad.

 

[pumaf1]

just for info - i only changed the filter and block after i lost the fish

oh well a nasty learning curve, but thanks to everyone for your help!