lump on goldfish

Question
i have one goldfish 5 years old about 5 inches. tank 125 litres. also one shabumbkin about 3 inches same age plus one catfish 7 inches same age.

i turned the light off and opened the lid of tank because we are experiencing very hot weather, hoped this would help to keep them cooler.when i turned the light on after two days because the plants need it my goldfish has an enormous lump one side of its head from the eye down past the gill  about the size of a marble( this was not there before i turned light off) the other two seem ok and the goldfish is swimming ok and eating ok . i change the water every two weeks and Hoover out tank every two to three days. can you give me any advice please.


Answer
Hi Norma,

Small bumps or tumors can be caused by various diseases and ailments, and judging by your description of the fish actively feeding, it's not a serious problem at the moment.

Could you please attach a picture to a followup question? There's a link in the followup question that says "Attach an Image". That way, I can correctly diagnose your Goldfish's problem.

At the meantime, perform 10% water changes daily, to help with recovery.
Your water routine seems perfect - keep up the good work!

Good Luck, and I hope to hear from you soon!