Hi sorry for late reply...
It seems that your tank is in the middle of cycling assuming because you still have a trace of nitrITE...So whats going on in short terms is there is enough bacteria in the tank to turn the ammonia to nitrite but not that much yet to turn it all into nitrATE. Nitrite is VERY bad for the fish and thats what is killing your fish. The ammonia obviously killed your gourami's, and than a little bit passed and the ammonia turned into NitrITE.
So since your tank is in the middle of cycling and you already have a good stock in the tank, besides the guppy's dyeing ( I'm very sorry about that ! ), Do daily water tests on the tank and if there is any trace of ammonia or NitrITE than do immediate water change for the fishy's sake! And I also see the LFS gave you a starter to help cycle the tank which is a BIG NO NO. They have bacteria in there but not benefical, it will just die off after a while and thats why your tank was running good for a while when you put the fish in but than all went bad...I would not add any more guppy's or any other fish untill the results are at :
ammonia: 0
nitrITE: 0
nitrATE: under 40
Hope this helps!
Nick
It seems that your tank is in the middle of cycling assuming because you still have a trace of nitrITE...So whats going on in short terms is there is enough bacteria in the tank to turn the ammonia to nitrite but not that much yet to turn it all into nitrATE. Nitrite is VERY bad for the fish and thats what is killing your fish. The ammonia obviously killed your gourami's, and than a little bit passed and the ammonia turned into NitrITE.
So since your tank is in the middle of cycling and you already have a good stock in the tank, besides the guppy's dyeing ( I'm very sorry about that ! ), Do daily water tests on the tank and if there is any trace of ammonia or NitrITE than do immediate water change for the fishy's sake! And I also see the LFS gave you a starter to help cycle the tank which is a BIG NO NO. They have bacteria in there but not benefical, it will just die off after a while and thats why your tank was running good for a while when you put the fish in but than all went bad...I would not add any more guppy's or any other fish untill the results are at :
ammonia: 0
nitrITE: 0
nitrATE: under 40
Hope this helps!
Nick
