Hi everyone my gsp, sharkey is looking thin..I brought him home in sept.. He looked a bit thin then but quickly over the nest couple weeks put weight on. This past 4 days I noticed him looking thin again..a bit pinched in the sides. I'm really worried I dont want to lose him.

from all the reading I'm doing on here I think he might have an internal parasite. What could you recommend buying to treat him? I've found somethings in Foster and Smith called Bi Furan+ ,Metronidazole,Para Gurad,Metro+,Probiotic marine Guard,Formalin,prazipro,fluke-tabs,parasite clear,ultra cure PX..Would any of these work for the parasite gsp get?
I keep sharkey in a 29 gallon tank..
Ammonia- 0
Nitrites - 0
nitrates- 10
PH-8.2
s.g-0.012
I feed him frozen bloodworms,mysis shrimp,freeze dried bloodworms and freeze dried krill.(snails daily) I faithfully do water changes on thursday.Thanks for any help you can give me.i really love this little fish.

mornings on all my tanks.