black male molly

Question
We have a 55 gallon tank at 78 deg.  The filter is a topfin 6.0 with 2 filters.
I am changing 10 gallons of water every other day.

We have:
6 black skirt tetras
6 longfinned zebra danios
6 harlequin rasboras
5 dwarf suckermouths
2 black molly (1 male 1 female)
2 silver molly (1 male 1 female)
2 african dwarf frogs

My problem is the male black molly is attacking the male silver molly.  He bites
the silver molly's dorsal fin and has taken a small chunk out.  I have caught
and separated him from the rest of the tank.  Is my tank too crowded or am i
doing something else wrong?  

Thanks

Answer
Hi Sandy,
  Your tank sounds like it is doing just fine and is not overcroweded.  There is very little you can do about the molly situation; basically the male black molly is trying to tell the silver male molly that he is the boss of the tank (and the females) and that is why the black one is biting.   

-- Ron
  rcoleman@cichlidresearch.com
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