fish disaster

Hi all

A few weeks ago we noted the out break of a fungal infection in our 4' -190lt
tropical setup. The tank is/was stocked with mostly S American a mix of tetras
and 5 corys, 4 large clown loaches for snail control and a solitary
bristlenose catfish. We checked our ancient copy of Axelrod and found that it
was only infectious to ill fish and shouldn't bother any others. Over the last
2 weeks we lost only a few tetras. Two days ago we purchased 12 rummy nose and
12 harlequin rasboras (sp?) to restock. We treated the tank with a commercial
treatment called Pimafix which is supposedly all natural -it seemed to have a
lot of tea tree oil in it. The dosage was only 40mls for the entire tanks (4
teaspoons).We came home last night to find ½ the tanks dead. I did an
immediate 25% water change. During the evening we lost the remainder of the
corys. Tonight we finally lost the bristlenose that had survived so much with
us - it was like losing a member of the family. We also found the last loach
dead as well as 4 of the rasboras. We are down to only 10 harlequins in the
tank.

Tank ph is 7 - temp is 24C - no nitrites or ammonia according to the test kit
I have. My question is what the heck can kill so quickly in such a stable
tank? We have had fish breeding in this tank and it has been running for over
5 years. This loss has been devastating. Any ideas - please reply here or to


thanks