dying mollies

Question
I have a 29 gallon tank with a variety of community fish. The tank is fully cycled and I decided to add new fish this last week. On monday (before I added new fish) one of my mollies mysteriously died. On wednesday I added two gourami's and all was fine. This morning (sat) my two remaining mollies were ok. When I got home from school around 3:30 I noticed that one of my white mollies had a swollen and red lip/mouth area. I called a fish specialty store to get immediate feedback. Together, we came to the conclusion that it was probably a cut and it was suggested that I just add a little extra slime coating to help with the healing. It is now 11 pm and I just got home again and the molly had died. When I took her out of the tank I was trying to look closely to see what had happened. It appeared as if there was a "blood spot" on top of her head but on the inside. I could see lots of red spotty stuff and a bit of green inside of her head. What could this be? I know I'm supposed to be worried when fish die off and I have checked my water a few times withing the last few days since the first molly died. Everything is perfect. I'm going to to a water change as soon as I wake up in the morning. Are my other fish in any danger? Is there anything else I should do besides the water change? Thank you in advance for your advice.  

Answer
Hi Marisol
That's a strange one.  Were/are any of the fish showing any symptoms like rubbing on objects, lethargic, gills moving fast, flashing, darting, gasping at the top of the water surface?  They were/eating ok?  And the red blood spot, was it like an open sore or ulcer?  

That seems kind of quick for the fish to go from fine, to a red mouth, to death with a red blood spot/sore on it's head.  It could be a bacterial infection, but it almost sounds like an injury to me, not knowing if there's other symptoms.  Sometimes gouramis can be aggressive, especially the regular varieities(non dwarf).  

What's your water parameters reading-ammonia, nitrite, and nitrate?  I would keep a close eye on the tank for now, and look for those symptoms I mentioned above.  Also, keep an eye out for aggression.

Let me know if you have any more problems!

Christy