nipping, ramming, and black spots

[EliK]

I'm relatively new at this. About 3 months ago, I started a new 15 gal. aquarium. Currently, I have a female molly and two fry, a male and female platy, one angelfish, a small bottom feeder (I don't remember the exact variety - the guy in the store recommended it), and a juvenile iridescent shark (someone gave it to me without me knowing what it was. now I'm working on getting rid of it).
All the parameters are normal, as far as I can tell.

Over the last week, I have noticed three issues:

1) The angelfish has become extremely aggressive, especially during feedings - chasing all the other fish away from the food.

2) The molly, in turn, has begun ramming and nipping at the iridescent shark, often for up to 10 minutes at a time.

3) I've noticed that the molly has developed some black spots, that I'm pretty sure were not there when I bought her. The angelfish also has some spots, but they look different, and I think they were there before.

I would appreciate any recommendations on any of these issues.
Thanks

 

[Colin_T]

Hi and welcome to the forum

The angelfish has matured and is establishing a territory and probably wants to breed. This is why it is chasing other fish away from its area and during feeding.

The molly needs to be moved out so it doesn't kill the iridescent shark. And you need to try and find the shark a new home asap, which you already know.

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The black spots look like Black Spot disease (Diplopstomiasis).

Try to find a dewormer for fish and treat all the fish at the same time. Look for Praziquantel or Flubendazole at the pet shop.

Remove carbon from filters before treatment and increase aeration/ surface turbulence to maximise oxygen levels in the water.

You treat the fish once a week for 4 weeks. The first treatment will kill any worms in the fish. The second, third and forth treatments kill any baby worms that hatch from eggs inside the fish's digestive tract.

You do a 75% water change and complete gravel clean 24-48 hours after treatment. Clean the filter 24 hours after treatment too.

Treat every fish tank in the house at the same time.

 

[EliK]

Thank you
I'll look out for those medications.
In the mean time - I've already found a place to move the iridescent shark out. The molly is still in the tank. While the molly has only started this recently, the shark has seemed lethargic and sickly since I got it.
I visited a few fish shops in my area today, and asked around about the black spots on the molly. They all gave me the same response, but I'm skeptical about it - I'm curious if there could be any truth to this. They said that do to the hardness and naturally high pH of the tap water in this area - between 8-8.2 - the skin of the fish gets discolored. I treat my water with pH down, but it doesn't seem that the store here do the same. Looking around in the stores, I did notice that all of the orange mollies had these spots, but no other mollies - even sharing the same tanks - had them. Does this ring true?
Looking at the fish more carefully - the spots on the molly are also very different than those on the angelfish. The molly's spots are raised, while the ones on the angelfish seem to be inside the flesh.