Lump on Goldfish

Several months ago my red cap oranda developed a lump on his side. It resembled an acne nodule. The lump was beneath his scales and didn’t seem to cause him any trouble. He had some mild red streaking in his tail which cleared up once I began doing more frequent water changes.

Recently, the lump has swollen. In fact, it looks like there are two smaller lumps beside it. The scales are pushed up and the area is red. See photos below.

Today the lump ruptured and briefly suppurated a stringy white tissue. Despite the lump and the rupture, the goldfish is behaving normally.

At first I suspected this was a tumor, but the rupture has me thinking otherwise. Can anyone with experienced help me diagnose the problem and advise me how to resolve it?

Tank Specs:

• size: 35 gallons
• fish: 1 red cap oranda; 1 black telescope
• food: flakes/peas
• nitrate: 20 ppm
• nitrite: 0 ppm
• hardness: 150 ppm
• chlorine: 0 ppm
• alkalinity: 80 ppm
• pH 7.2
• ammonia: between 0-0.25 ppm (I use the API test kit which isn’t super accurate.)

Action Taken:

I’ve already done a five day treatment on the tank using Marineland’s All-In-One Remedy, since I’ve had luck with this product in the past. I’m also doing 1/3 tank partial water changes every other day in an effort to keep the water pristine.

Photos:

(I’ll update the photos if I can get some better ones.)