RIP "Molly"the mollie :(

[MollieBeginner]

My 3yr old has a best friend that got him to sleep in his own bed for past 2 weeks!!!! Today we went to feed her and she was in a white fuzzy "sleeping bag" And there are pieces of the fuzz floating around. I must replace her before he realizes, but 1st I want to make sure I do everything right for "molly" #2. I also want to make sure that my kids are not in any danger should cross contamination occur. I've done tons of reading but it's not conclusive, I'm only speculating it's strain 1 columnaria. It was fast! Like 8 hours she was encapsulated with the fuzz. Do I boil contents of tank in salt water? Do I cycle peroxide thru tank then boil contents? Do I need to make sure kids don't help or touch water? How long or how many times do I cycle? HELP!!!

 

[seangee]

Do you have a photo.

 

[Essjay]

We do need some more information. I know you are so relieved that your son actually sleeps in his own bed now, but you also need to think about the fish.

How big is the tank?
How did you prepare the tank before getting the molly?
Does the tank have a filter and a heater?
How often did you change the water in the tank, and how did you do it?
Have you been testing the water for ammonia and nitrite?
Is your tap water soft or hard?


I will explain why I ask those questions.
Mollies are big fish, females can grow up to 6 inches. They need a tank at least 36 inches/90 cm long.
There are lots of micro-organisms that live in a fish tank but they take a while to grow. The most important ones are those that 'eat' the ammonia that the fish excretes. The best way to set up a fish tank is to add ammonia from a bottle before any fish are put in the tank. This ammonia feeds the few bacteria in the water and gets them to grow over a few weeks so that when the fish are put in there are enough bacteria to 'eat' all the fish's waste. If this is not done, and fish are put in the tank straight away, ammonia builds up in the water and poisons the fish. The fish keeper needs to do lots of water changes to remove this ammonia until the bacteria have had chance to grow.
There are actually two lots of bacteria. One 'eats' ammonia and turns it into nitrite. the second 'eats' this nitrite and turns it into nitrate. Both ammonia and nitrite are poisonous to fish. This is why I asked if you have been testing the water for these things.
Mollies are tropical fish, they need warm water at about 25 deg C/77 deg F. And a filter is the best place for the ammonia and nitrite eating bacteria to live.
Different fish have evolved in different kinds of water. Some fish evolved in soft water so they need to live in soft water. others evolved in hard water. Mollies are hard water fish and they get sick very easily if they are kept in soft water.




I know you asked about how to clean the tank ready for another molly but you really do need to think about whether getting another molly is the right thing to do. If you have soft water, for example, molly #2 will also die quite quickly. And I suspect the tank is quite small since it is in your son's bedroom.
If you could answer my questions we can help you keep fish successfully for your son, though it may have to be a different type of fish.