new cories died... my fault?

[Bathos]

after waiting for my 10gal tank to cycle (i was doing fishless cycling), i went to my LFS to see what they had. i've been wanting to breed C. trilineatus again for some time, but didn't think it was fair to the fish if i wasn't settled first. i saw 3 C. trilineatus, all fairly active, with no signs of disease, and no diseased tankmates. i asked at what pH the cories were kept and was told 7.0. i took the cories home, cut the top off the bag and floated the bag in the tank, attaching it to the top of the tank to make sure it wouldn't tip over. i gave the water in the 10gal one final test. pH 7.4, no ammonia, no nitrites, no nitrates (i had just done a water change). concerned about the .4 difference in pH, i used a large eyedropper to give the bags a few squirts every 5 minutes for the next 2 hours. the cories still looked fine. i netted the fish from the bag and transferred them to the tank. an hour later, one of the cories was tipping on to his side. another of the cories was resting near the top of the water. i added an airstone. a few minutes later, the fish resting near the top of the water was floating around with his mouth at the surface of the water and the rest of his body hanging straight down. at this point, 2 fish on the bottom are lying on their sides and the stomach area just behind the gills is getting a metallic look. i looked closely at one and it was bleeding from the part of the body where the fin attaches, and later started bleeding from the gills. i sat some nets in the tank and put the survivors in there. i am now left with one out of the four i started with last night. what went wrong here? was it something i did, or were they already ill at the LFS?
-Liz

[STINGRAY]

Was the water conditioned at all? Your lfs should replace fish if your water was ok and not at fault. Sometimes we have problems like this with corys when they come in and quarantine accordingly using mild bacteracides. I am sure some of the fish we have lost in the past have had symptoms you describe. When you say bleeding around the gills do you mean a large red like sore or actual gill imflamation?

[Bathos]

yes, the water was conditioned using Aquarium Pharmeceutical's tap water conditioner, which removes chlorine and chloramine and detoxifies heavy metals. the LFS has offered to replace the fish. when i say bleeding around the gills, i mean the gill would turn pink, then bright dark red and be swollen (but you could still see the gill covering on top of it all, so if there was a sore, it was under the gill covering) and a little bit of blood would come out. it was horrible to watch. i felt so bad for the poor fish, but didn't know what to do.
-Liz

[oneoddfish]

I HAVE TO SAY THOSE FISH WERE ALREADY DYING. IF YOU'R WATER WAS FINE EXEPT A SLIGHT DIFFERENCE IN PH. I TRULY DON'T SEE IT HAVE THAT EFFECT.I WOULD HAVE STORE REPLACE CORY'S IT'S NOT YOU'R FAULT!!!!

[Dinyar]

Reddened gills are also a sign of nitrite poisoning, which would be consistent with a tank that has only cycled partially.

Dinyar

[Bathos]

and i'd consider that as the most probable thing if the nitrite hadn't tested 0, both with my test kit and the test kit at the store. this is really strange. i've never seen anything like this. i do want to make sure it doesn't happen again, but i'm not quite sure how to do that if i don't know what was causing it. now i'm a little leary of getting more cories with my store credit.
-Liz

[Graeme]

Hmm! Maybe your lfs was telling a little lie about their pH?

[oneoddfish]

I don't mean to get off topic BUT would ph have that negative of a effect if it was say 8.0 instead of 7.0 wouldn't there have to be a great difference like going from say 8.5 down to6.0 ??

[Rusty]

Each whole number increace in the pH scale is 10 times higher than the previous number. For instance, 6.0 x 10 = 7.0 . So yes, I do think it would be a drastic change.

Rusty

[STINGRAY]

Cory cats are usually quite hardy and will tolerate a slight variation in water quality, They are found in a variety of conditions so I don't think the water parameters are at fault, unless as said the ph was way off. The more likely cause is still bacterial or parasite infestation.