Based from the information you have given me above I think the only possible explanation would be stress from transport. All of my water parameters are where they should be but my acclimation was just floating the bag. Would you recommend the drip method for the future? My ph is quite high at 7.8, I use drift wood to stabilize it. As far as the condition of the corys when I got them I don't know because I got them from big als which is two hours away. The loss was gradual as I lost one fish at the start and a couple about a week or so after I purchased them.
Thanks for all your help
@Byron
The stress caused to fish that are chased around the store tank, netted, bagged, transported home, then placed in a completely new/different environment is severe. It triggers the "escape from predator" response, and this is as severe as stress can get to a fish. Obviously we cannot eliminate all this stress, but we can take steps to minimize it.
My method for acclimating new fish involves floating the bag for 10-15 minutes to equalize temperature. Sometimes I carefully remove some of the bag water first, depending how much there is, so that I can mix tank water in after the temp has evened out. I then add some tank water to the bag, maybe a cup, sometimes less depending upon the delicacy of the species. I let this mix for 15-20 minutes, then add another cup of tank water. I might do this three or four times, again depending upon the species. Then I net the fish out of the bag into the tank. Never pour water from the bag into the tank; there may well be pathogens in the water you do not want in your tank. This process I do in my QT tank. Some people use a drip method, dumping the bag (water and fish) into a pail, then dripping tank water into the pail for a couple hours, then net out the fish into the tank.
Some will say the above mixing of tank/bag waters is not needed, and once temperature is equal, net the fish into the tank. I've always taken the time to do the mixing.
How you transport fish is important too. I have a small cooler that has two important advantages: it maintains the temperature (avoiding cooling in winter and heating in summer) and it also keeps the fish in the dark. This latter is more important than many realize; fish in darkness are more relaxed.
Stress can harm the fish's physiology, and even if fish seem to live through this, it has taken its toll and it may be weeks and even months before the fish suddenly dies. At the very least, stress weakens the immune system, and this means the fish may succumb to some disease down the road that it would normally be able to fend off.
The pH of 7.8 is not too bad, but the more important parameter is the hardness. The GH directly impacts fish metabolism and physiology, and the related KH (Alkalinity) can too. These also impact pH.
Byron.
