Carbon Pellets Kill My Fish?

[KawaiiFish]

So, I have just bought a Kent Marine Bio reef aquarium and it came with a netted bag of carbon pellets? When I rinsed them in the sink all the water was black. I did put them in the back of the filter as in my other tank I have a filter sponge and carbon sponge thing in there as well so I though I was doing the right thing? However, I had a green spooted puffer in there who I was going to convert from fresh to brackish water. He died after a day of the carbon being in. However, he looked like he had a mouth fungus so don't know if he died from this or the carbon? Iv two mollies in there now and scared they will die! Should I leave the bag of carbon in? Was it meant to go into a protein skimmer? As I don't have one of these? So many questions but I'm not sure what to do now Hope someone can help!

 

[WILDER]

You only need to use black carbon for removing medications from the tank.
Black carbon only effective for 2 to 9 days.
Just remove the carbon pellets and throw them away.
Using black carbon all the time is a complete waste of money.

How many gallons is the tank please?
What are your water stats in ammonia, nitrite, nitrate, and ph?
When you bought the puffer fish from the LFS was he in brackish water, or freshwater.
How long did you climatize the fish for?

Columnaris (Mouth Fungus)
The fish will have white cotton strands around the mouth area, Or cotton wool patches around the mouth.
Was the mouth rotting away?