[Supa Samoan]

I don't think it's hydra... Those usually appear in planted tanks along the walls, driftwood, and are not found on the fish itself.

It's most likely internal parasites (hexamita). It's can be spread when other fish "mouth" infested feces from another infected fish. The initial symptom is white stringy feces which actually looks transparent and hollow. In its advanced stage, the fish will stop eating and waste away. The recommended treatment is with food soaked in metronidazole. Bumping up the temp will increase its efficacy but increase aeration while you do this.

[snapback]870549[/snapback]​

It sounds like this is the case it's very treatable but act quick.gl