My Blck Cory is dead!


Guru Class Expert
Jun 15, 2009
Hi all,

My Black cory was found dead this morning, and half eaten. All the other critters seem ok, apart from one of my SAE's, his black stripe has gone faint.

I am putting it down to my co2, i increased it and all the fish went to the bottom.

Is it ok to have good surface movement and high co2 and maybe inject o2 as well. Or should i stick with low surface movement and reduce my co2


Plant Guru Team
Lifetime Member
Sep 23, 2007
South Florida
With higher c02, more 02 is required..... better surface movement and more 02 will allow for more c02.....

Or option 2 will also work.........

IMO, more 02 is NOT a bad thing, esp when injecting c02.....

Sorry to hear about your fish.......


Lifetime Charter Member
Lifetime Member
Jun 21, 2009
Surprise, AZ
I Think The CO2 Is Fine.

Hi Geoff,

I am sorry to hear of the loss of your Cory. :(

I need to point out that it is unlikely bordering on impossible to kill Callichthyids with CO2 or low Oxygen saturation. Many of the “catfish” breathe air when water conditions are poor; Callichthyids breathe air anytime they wish.

Further, the fish behavior of the fish “going to the bottom” is inconsistent with signs of CO2 toxicity or oxygen deprivation.

The first sign of hypoxia in fish is actually lethargy; you mammals expend 1% or so of your energy on respiration, whereas fish expend 10%.

Among the most common error in fish keeping is considering lethargic fish ill (diseased), medications are added often further decreasing O2, reinforcing the idea that the fish are “sick.”

Many do not recognize hypoxia until the fish are gasping at the surface. a nice primer on respiration. More for the aquaculture community but page 11 or 12 starts an interesting and pertinent piece on fish and respiration. a “down and dirty” guide to fish respiration

Would you care to tell us more about your aquarium? Perhaps we can figure out what happened.



Guru Class Expert
Jun 15, 2009
so am i right in thinking, my fish went to the bottom of the tank due to poor oxygen levels. The level of oxygen increases as the depth increases?

My black cory did not die from oxygen deficiency as they can breathe air at very low o2 levels.

I will introduce surface movement with my koralia.

The black cory was only a few months old form my LFS, the other corys in my tank are fine and i have had them over 1 year.

My cherry and bumble bee shrimp bred recently :) they all seem fine.

My tetras look ok as do my endler guppies.

My SAEs seem ok, but the largest of them has a faint black stripe now instead of his usual black stripe.

I run my tank at a pH of 6.3 with CO2 and dose EI with added MgSO4 and excel daily.

I get a bit of algae but the SAEs seem to like it.