My gold fish is unable to swallow food

[Elgin loon]

One of my goldfish will take her food, chew it for a while up then spit most of it out. She spends most of the time on the bottom, apart from feeding and making a dart to the surface for air.

180litre tank. 2 1yr gold fish. All water levels are good. No sign of disease. In ok condition though lost some weight now.

Planning on capturing her and opening her mouth to see properly inside, incase there is a blockage. 

Any other ideas?

[koko]

May have Flukes have you ever treated your tank with Prazi? 

[Arctic Mama]

Hey there  some pictures or video of your fish trying to eat and the tank as a whole would help us. It could be a mechanical blockage, but we are going to need images and many more details to help out. Long distance diagnosis is tricky without those

Test Results for the Following:

* Ammonia Level(Tank)

* Nitrite Level(Tank)

* Nitrate level(Tank)

* Ammonia Level(Tap)

* Nitrite Level(Tap)

* Nitrate level(Tap)

* Ph Level, Tank (If possible, KH, GH and chloramines) 

* Ph Level, Tap (If possible, KH, GH and chloramines)

Other Required Info:

* Brand of test-kit used and whether strips or drops?

* Water temperature?

* Tank size (how many gals.) and how long has it been running?

* What is the name and "size of the filter"(s)?

* How often do you change the water and how much?

* How many days ago was the last water change and how much did you change?

* How many fish in the tank and their size?

* What kind of water additives or conditioners?

* What do you feed your fish and how often?

* Any new fish added to the tank?

* Any medications added to the tank?

* List entire medication/treatment history for fish and tank.Please include salt, Prazi, PP, etc and the approximate time and duration of treatment.

* Any unusual findings on the fish such as "grains of salt," bloody streaks, frayed fins or fungus?

* Any unusual behavior like staying at the bottom, not eating, etc.?