Originally Posted by frogman1980
now the questions...
1 what could be causing everything except the betta to die.
2 how can i fix it.
3 are there other fish i can try.
and 4 they had a version of cory cat that is a little smaller. will they mix with the ones i have already or should i treat them like a different school?
Well, you've got some seriously contaminated wood, there. I wouldn't use it in any tank at this point.
I do know that wood sold for aquariums and wood sold for reptiles are different; any chance this was in a reptile tank, not a fish tank?
Copper will kill off shrimp quickly.
Test the pH with the wood in there, wood can seriously drop the pH. Since you had an issue with the corys as well, I would suspect this. I have one piece of driftwood which was seriously dropping my pH levels, as well. I put a net bag of crushed coral in the filter, and that stabilized the pH, so I could keep using the piece of wood.
Do you have any way to backtrack and learn what the wood is? Mopani, Malaysia yellow, etc. They each have their own traits, and belong in certain biotopes ONLY.
Now your last ? - mixing cories. They will school together because they have no choice. Cories are schooling fish. They much prefer their own type, and will be happier, feel safer, and thus be healthier, if you stick to one variety.