Yes, it is a bacteria infection... it causes buoyancy problems and needs treatment in QT with Diomax which you need to get from vet or find place to send away for. When I had them, I sent away to England for it.At first I thought you were holding a bristle worm and you named him bubble tail! Then after looking back at the first photo I saw the head of the pony. So does that make them sick?
Seahorses are very dirty fish. Food goes right thru them. As soon as they eat, they poop so constantly keeping up on keeping the perimeters good. That is why it is recommended to have at least 30 gallons for 2 seahorses and additional gallons after that.Do you know what causes the bacteria infection?