Dwarf Neon Blue Guarami -dead :(

Question
I have a well established (3years) densly planted 25 gallon aquarium.  I have 2 3yr old clown loaches and 4 3yr old glass cats in my tank.  I bought 2 neon blue guarami's yesterday and added them to the tank.  They both looked very healthy when I bought them at the store.  I put them into my tank (after letting them acclomate for 1/2 hour in the bag they came in).  One was literally swimming in circles within 4 hours and died after only 6 hours.  I would have brought him back immediatly, only the pet store was closed.  The other guarami appears to be doing very well after 22 hours in my tank.  Why did the one die so quickly? -All my fish seem very healthy, -no bacteria/parasites, etc.


The only thing I can possibly come up with is that the one guarami swallowed too much CO2.  I have a CO2 canister that feeds CO2 to my live plants.  I've had this set up for 3 years and all the fish have seemed to be fine w/ it.  I have plenty of air bubbles in the tank, some surface tension from the out of tank filter and a densly planted tank (so plenty of oxygen)?

Any idea of why a fish would die so quickly after putting it in my tank (when all the other fish are doing great)?  -this fish looked really healthy when I bought it and for the first several hours in the tank.

Answer
Well my thought is this eric,

You might have just got a bad fish, maybe he was stressed out as it was from his previous journey and now this was just another stressfull period for him and he just died. We cant figure out exactly why fish die all the time. This seems to be a random occurance so it's not affecting other fish right?

The first could have been stressed or maybe his health was poor prior to this. those are my best assumptions, i notice it somtimes when i get new fish and he goes and hides by himself for a while... then i know that he's probably a bad fish already... these things just happen, choosing healthy fish from the start can somtimes avoid these situations :)

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