Wate change== dead corys!!

I did my usual water change yester day and ALL my corys are dead. Do not know why....

Tank is a 100gal. Was torn down and re-setup in late MAY/early June. Heavily planted. In tank is about 85 tetras and others (Diamond, Bleeding hearts, Cardinals, Head and tail lights, Black phantoms, with 15 gold barbs, 4 angles, 6 Columbian rams and 8 ottos).

The tanks has (had) 6 Cory Robineas (the flag tails). All have done well till this morning. I did my usual water change (about 25gals). Used "Prime". All other fished are doing fine.

Any ideas??

PSS.. I have been keeping fish for over 40 years.

greendeltatke said:

I'm sure you know alot more about this than i do, but... I read some post a while back from someone who lost his bottom dwelling fish because he disturbed some anaerobic pockets in his gravel. His gravel was very deep (5 inches) and he had only skimmed it for a long time. Then one day he did a deep cleaning, really stirred the gravel around, and lost his bottom dwellers. Is that a possibility?

Click to expand...

I am not sure. My gravel bed is no more then 4+ months old. When I change water (because I have so amny plants) I usually only go down about 1/4 to 1/2 inch.

TKOS said:

Did you test the water to see if there was some sort of ammonia or nitite spike? Did the pH fluctuate for some reason?

Click to expand...

Did not check for ammonia or nitrite spike, but because I have a school 15 cardinal tetras I assumed that they are more delicate. Did not lose any tetras of any kind.

I have an electronic PH monitor on my tank. The PH was 6.7 before water change. Was 6.9 after the change. My CO2 keeps it at about 6.7