Strange Acting Corycat

[fluttermoth]

I would do a big water change, check your filter (but don't touch it unless it looks like it might get/be clogged) and leave the fish without food.
 
They can easily go without food for a couple of weeks, so a few days won't do them any harm, and it's better than risking novices overfeeding.
 
I've never had problems with cories or loaches on play sand, just this black stuff that turned out to be a volcanic one

 

[SamB]

Just out of curiosity, what was it about the sand that was bad for them?
 

 

[eaglesaquarium]

They can easily go without food for a couple of weeks, so a few days won't do them any harm, and it's better than risking novices overfeeding.

 
 
+1,000,000!!!
 
Exactly.  No food is better than too much food, especially if you are dealing with an ammonia issue (which may or may not be the case).  Overfeeding will lead to an ammonia problem!

 

[SamB]

Ok, I will let the guys know. That's also good to know just in general.

 

[the_lock_man]

I've never had problems with cories or loaches on play sand, just this black stuff that turned out to be a volcanic one

 
Oh! What did it have in it, then, plenty of sulphur, presumably?

 

[fluttermoth]

I have no idea what was wrong with it
 
All my tests came back normal; I hadn't added anything different to the tank, except the sand, and they were established fish I'd had for years in other tanks. It only affected the catfish; the neons and hatchets were all fine.

 

[the_lock_man]

I have no idea what was wrong with it

 
All my tests came back normal; I hadn't added anything different to the tank, except the sand, and they were established fish I'd had for years in other tanks. It only affected the catfish; the neons and hatchets were all fine.

 
Presumably then, something solid within the sand (and if it's volcanic, then as I say, sulphur would be my guess, but could be a few other things as well), that the cories were ingesting, rather than something dissolving into the water.

 

[SamB]

Unfortunately I have just come home to one very dead corycat  

 

 
What do I need to do for the other fish??

 

[eaglesaquarium]

50% water change...
 
Sorry...

 

[mark4785]

Unfortunately I have just come home to one very dead corycat

 

 

 
What do I need to do for the other fish??

 
Test your KH, GH and PH of your tank water and tap water. If the values are exactly the same, remove the fish to a temporary holding spot with a heater (with heat guard) and remove 100% of the main tanks water to remove the ammonia and prevent an eventual nitrite build up.
 
If your KH ,GH and PH values vary, do several 25% water changes (every 4-5 hours) until you reach an ammonia reading of 0 ppm. If your API ammonia testing kit is hard to interpret I highly recommend the Nutrafin ammonia test as the solution is transparent when no ammonia is present and is colourful when ammonia is present.
 
Cut down on feeding by 66% and gradually increase the amount fed over a long period of time.
 
While you are experiencing problems with ammonia I'd definitely advice you sucker on a Seachem Ammonia indicator card as this will alert you to an ammonia build up.
 
Note: Be mindful of your GBR's when doing your water changes as these will be the first to react to fluctuating GH and KH values. Their reaction is typically death.