Platy losing weight, hiding, not eating and head turning black in places.

[Helpmyfish]

My approx 6 month old male platy is loosing weight, is lethargic and not eating is also hiding and his head is turning black in places. He was flashing and scratching a few months back without these current symptoms and the whole tank was treated with anti-parasite medication which seemed to sort the problem. He shares a tank with 4 Danio of a similar age. He did have a Platy friend who died about 3 months ago. All fish are male. I don’t have a hospital set up but have Removed him to a temp make shift tank with about 2 litres partial tank water and new treated water. This wa only done as he was literally at deaths door. Still not eating. He’s balanced in the water. Will swim a little. Mostly just sits there. Fins are not clamped. Breathing not specially erratic. No visible signs of rot or fungus.
Help!

 

[FishFinatic77]

Can you post a picture and maybe a short video of him? That might help us to figure out what he might have.

 

[Salty&Onion]

Is a picture of the fish and a 30 second video possible?
What is your KH, GH and pH? This can be found on your local water providers website.
I want to just throw in, danios need to be in groups of 6 or more as they are schooling fish.

 

[PheonixKingZ]

Yes, we need to know your pH, GH, and KH. (We need actual numbers.)

 

[Colin_T]

What does the fish's poop look like?
If it's white and stringy, see below.

Fish do a stringy white poop for several reasons.
1) Internal Bacterial Infections causes the fish to stop eating, swell up like a balloon, breath heavily at the surface or near a filter outlet, do stringy white poop, and die within 24-48 hours of showing these symptoms. This cannot normally be cured because massive internal organ failure has already occurred.

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2) Internal Protozoan Infections cause the fish to lose weight rapidly (over a week or two), fish continues to eat and swim around but not as much as normal, does stringy white poop. If not treated the fish dies a week or so after these symptoms appear. Metronidazole normally works well for this.

There is a medication (API General Cure) that contains Praziquantel and Metronidazole.

It's interesting that API and the Californian government have listed Metronidazole as a carcinogen. That's a concern considering it was widely used to treat intestinal infections in people.

Anyway, if you use this or any medication, handle with care, don't inhale the medication, and wash hands with soapy water after treating the fish or working in the tank.

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3) Intestinal Worms like tapeworm and threadworms cause the fish to lose weight, continue eating and swimming normally, and do a stringy white poop. Fish can do this for months and not be too badly affected. In some cases, fish with a bad worm infestation will actually gain weight and get fat and look like a pregnant guppy. This is due to the huge number of worms inside the fish.

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Black patching on parts of the body is normally caused by chemical burns (ammonia, nitrite, nitrate, chlorine/ chloramine, medications, etc).