I bought a baby calico rancu goldfish about four days ago. On the first day he seemed fine he was active and seemed fine until the next day when I feed him. as soon as he ate a pellet(Hikari lion head)he got super lethargic and just sat for a long time and he's been doing the same thing since. every once and a while he will do a lap around the tank and then go back to the same spot and sit just above the gravel. when he sees food falling he goes after it and gets 1-2 pellets but as soon as it hits the gravel he loses interest. he hasn't pooped much but the little that he has done starts with a clear stringy mess and ends with a small light brown poop. This sounds like internal parasites from what I've heard but I'm not 100% sure. If you can identify the sickness from this if any what meds would you recommend?