HI guys I have 3 GBRs in my main aquarium, I added them after 2 weeks of quarantine just a couple of days ago. However since then one of them has fallen very ill and the others are also showing signs of the same illness. Basically the only visible symptoms are rubbing against objects, increased breathing and a motion I can best describe as shaking their back fin. Later on the fish isolates itself, its gills swell up and breathing is very rapid, then it dies. Does anyone have any idea what this could be ?