Dieing Minnows

[samyboy]

well a short while ago the minnows seperated and wouldnt school together 3 would swim around the lower regions of the tank and the other 2 would swim around the top

i added a female betta to the tank the next night i found a minnow struglig for its life with no tail (i think she had that) and red marks all over it so i divided the 3gallon tank into to halfs for both betta's to live in there,

another minnow tonight had the same symptoms red spots and strugling around i carefully netted it as i did it frantically swam into the netting stunned itseld flipped onto its back and floated to the surface, 5 mins later (i isolated it to a bucket) it was swimming around again another 5 mins passed and it was dead,

thus leaving one swimming around te bottom till so i though he's going to be next togo ill isolate him from the other fish netted him and the same happened knocked himself out cold

the remaining 2 are fine and swimming together the cory's are better than ever and i think ones carrying eggs, also done a 25% water change, sorry no stats should i isolate the final 2 minnows before they take the same route?

any help appreciated

 

[WILDER]

Need water stats in ammonia,nitrite,nitrate,and ph.
Do the red spot looks like pin pricks as it sounds like septicemia.

Red spots on skin can be caused by:
Regarding the small red dot, small pinprick like haemorrhages (called petechiae) can be due to a local lesion, a generalised septicaemia or toxaemia caused by acute viral and bacterial infections.