oh dear...
what do you mean by "blood spots? are these red spots that occur where no scales are present or are they wounds that go through scales (like holes) or are they wounds beneath the scales leaking blood from beneath?
the tail-are there tears and rips, broken arteries, crushed areas of fin, or something else?
good job for you-it was a smart move to do a water change...
go to a pet store and pick up some melafix (small blue bottle, yellow and red label)-that will help your fish regenerate and slow the progression of any bacterial infection...
please be very specific when you respond, perhaps you could include a picture...