Large lump!

Question
Please help! I have a 2 year old goldfish, a Calico Ryukin. I just discovered a large lump on the his side! It looks like it is under his scales since it is not mis-colored or anything. The lump is about the size of the end of a pinkie finger and it is pretty oval shaped.( There is nothing coming out of it.) His attitude has completely changed. He has just sits at the bottom of the tank all day and rarely ever swims around. He is in a 20 gallon tank and has a tankmate, a Sarasha goldfish. My tank has a TopFin filter system. I change about 10+ gallons every couple of weeks. I just changed the water a few days ago. He was acting tired all week but I just noticed the lump today. Today i checked my water and the ammonia was 0, the nitrate was 0 and the pH was 7.0. Please help.

Answer
Hi Mikalia;

He may have an internal infection, a tumor, a cyst, or even be constipated or an egg-bound female. It is so hard to diagnose these kinds of internal problems in fish. If your fish is still eating you could try an antibiotic food in case it's an internal infection. Medicines added to the water just can't work very well in deep-bodied fish such as goldfish. It has to be taken internally or by injection from a veterinarian. You could also try feeding squished green peas for a few days in case it's a constipation issue. There isn't much else you can do except maybe take your fish to the vet. They can do much more such as take samples for testing and prescribe injections that we can't on our own.

Wish I could help more...

At Your Service;
Chris Robbins