I have one black moor fan tailed goldfish, in a 19l tank with a filter. In the last 2 days or so he has developed 3 small bubbles on his body; one either side of his top fin thing, and one next to his tail, they are shallow, and don’t protrude much. I have had him for about 1.5 months, and recently changed all the water and the gravel as I had another fish which died, and the pet store I got him from recommended I do a total clean. When I refilled the tank I put in tetra safe start liquid, which claims to make the tank pretty much instantly safe for fish. My question is, should I be concerned? I have tried to take a photo but it is not visible in the low light of my house.