Cory Deaths

[Spishkey]

over the past few weeks i have lost around 10 corys (albino and my rather expensive sterbais) yesterday alone i lost two.

i really cant figure out what the problem is? its totally different to the last time my corys got wiped out (suspected dropsy though very hard to diagnose in corys, lost 6 adults and 45 babies then )

i inspected the two bodies from yesterday very closely, and although they look in perfect fitness, just behind their head on the underside is totally caved in on both, there is no sign of internal parasites so am concluding they have starved to death although i see them eating daily??
yet they are fed a very good diet of sinking cory tablets and various veggies which they seem to pick at. ive inspected my last two surviving corys out of this group and they have no sunken in bits.
the sterbai that died yesterday also seemed to have a fit shortly before death? (it lay down on its back after seeming well then shock very violently for a few seconds,this subsided leaving its two side fins quivering then death shortly followed.

any idea why, how or what is happening with my corys?

sorry forgot to add tank stats
500L+ community tank, ammonia 0, nitrite 0 nitrate fluctuating between 5 and 20 (this is higher than the usual 5 but am doing daily water changes to keep this down cant figure out why it keeps rising?)

 

[WILDER]

What does it look like when the fish goes to the toilet.
Did the anus look enlarged or red and inflamed.

Do the fish that died bloat up slowly.
it could be bacterial or even fish tb.
Have you used a bacterial med.

Fish showed any of these symtoms apart from bloating.

Symptoms can include:

Loss of appetite
Progressive thinness
Sluggish movement
Folded fins
Eye protrusion
Dark coloration and granular appearance of the cornea (this is the first sign in Angelfish).
Skeletal deformity
Hanging at the surface
Skin defects, including blood spots and open wounds that may ulcerate
Black spots, or overall dark coloration (in Cichlids particularly).
Fin rot, characterised by the outer rays falling out.
Scales loosening and falling out
General swelling and scale protrusion (as in Dropsy)

 

[Spishkey]

What does it look like when the fish goes to the toilet.
Did the anus look enlarged or red and inflamed.

Do the fish that died bloat up slowly.
it could be bacterial or even fish tb.
Have you used a bacterial med.

Fish showed any of these symtoms apart from bloating.

Symptoms can include:

Loss of appetite
Progressive thinness
Sluggish movement
Folded fins
Eye protrusion
Dark coloration and granular appearance of the cornea (this is the first sign in Angelfish).
Skeletal deformity
Hanging at the surface
Skin defects, including blood spots and open wounds that may ulcerate
Black spots, or overall dark coloration (in Cichlids particularly).
Fin rot, characterised by the outer rays falling out.
Scales loosening and falling out
General swelling and scale protrusion (as in Dropsy)

none of the fish have bloated up? they look in perfect health, no loss of appetite, no progressive thinness, no sluggish movement/folded fins/ protruding eyes, no dark colouration of the cornea, no deformaty, no hanging at the surface, no wounds, no defects, no spots, no rotting, no loose scales no swelling or signs of dropsy (which in a cory is hard to diagnose but trust me i know the signs of that one after last time)no signs of parasites or worms, no swelling of the anus, no reddening, no rubbing or flipping (just the one i saw have a kind of spasam/fit just before death) no nothing to go on!

the only thing you notice is the caved in spot behind the head on the underneath after they have died.

 

[WILDER]

Sorry for all the questions just had to rule out internal parasites, fish tb.
Don't know what the corys died of but concaved heads can be linked to hole in the head.

I would maybe pm inchworm to see if she seen anything like it before.
She keeps alot of corys.