OP said 240L which is only 60G.
Yikes- this is cryptocaryon which is marine ich and mucus cones from irritation. How long has this been on the fish as this does not happen overnight and has been developing. Tank is likely infected as MnFish stated will have to be fishless and treat with Coppersafe or Copper Power at therapeutic level 2.25-2.5 For a FULL 30 days (do not interrupt this 30 day period) monitored by a reliable Copper Test kit. Also monitor Ammonia levels while in quarantine with a reliable test kit and add aeration during treatment using an air stone.Hi. I noticed yesterday my purple tang was covered in little white flecks, today it is much worse. I have noticed him covered more heavily. The blue tang has it slightly. I have 9 fish in the 240L DT which is where it's broken out. I added 6 of these fish from another person and upgraded lighting only a week n half ago. They had nothing on them then. Can anyone suggest my best way of tackling this problem?
I've just realised where it came from. I added 3 new corals sent from an aquarium this past Wednesday. It's only Sunday, can it spread that quickly?
I would say 'not usually'
While coral can come in with parasites and other foreign issues, its a slight maybe. Velvet on fish is often caused by a dinoflagellate parasite known as Amyloodinium ocellatum and often triggered by poor or no acclimation which will certainly place any fish at risk of bacterial, parasitical and viral issues. It takes several days for this and other conditions to be noticed/seen and has already progressed.
