Dark splotches on Powder Blue Tang


New member
Today, I got a medium sized Powder Blue Tang from my LFS. I noticed that it has some dark splotches towards the tail fin on one side. Is this a cause for concern? :sad2:

Photos for reference:

  • 75 gallon with 20 gallon sump.
  • 4 Months old.
  • Cycled with cured life rock, live sand, bio-spira, stability and two medium clown fish.


  • Salinity: 1.025 (ATC Refractometer)
  • Temperature: 80F
  • PH: 8-8.2
  • Nitrate: 0
  • Nitrite: 0
  • Ammonia: 0
  • Phosphate: < 0.25 (It's hard to read)

Last fish added:
Today, Tuesday at 2pm the pictured Powder Blue Tang was added.

It was not quarantined.:jester: I know this is a really good idea going forward. I don't have the resources currently and my girlfriend would really like fish in the tank :)

I live 5 minutes from the LFS. To acclimate, the bag was submerged in the tank. Every 5 minutes, for 30 minutes (6 times), 8 oz of tank water were poured into the bag. The bag was emptied and the fish dropped into a bowl of tank water. It was then dumped (without using a net) into the tank.

There are dark splotches towards the tail fin on one side of the fish (at certain angles, they disappear, see photos).
No visible white ich.
No visible damage to fins or gills.

Since introduction to tank, it has been picking at algae on the rocks and heater. It ate frozen food shortly after being added.

The fish is actively swimming at all levels of the tank. It does not appear frantic and has proper buoyancy. It has a healthy appetite and did not show any signs of severe stress (shortness of breath), limited movement.

Thanks for reading!!


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New member
It is difficult to say what exactly it could be with the pics provided. At times it seems like a shadow, but in other positions it seems like how you describe it. QT is essentially, especially with disease-prone fish. Tangs, in particular, can be ich magnets (obviously not all tangs have ich, they seem to be more susceptible to it). Powder tangs, in my experience, almost always develop ich. If it were me, (other than the fact I would have QT'ed in the first place), I would take out the tang and put him in QT. It doesn't even have to be another aquarium....a rubbermaid with heater, filter, and maybe a protein skimmer (not totally necessary) would be sufficient.
I understand the excitement of wanting to have fish in the tank, but think of it this way: would you rather QT for a month or have to leave your DT empty for 72 days to rid the tank of ich...
I would QT, do TTM (many good threads here on the method) and complete prazipro dose in case of internal parasites.
Frankly, you will need to treat your clowns as well and leave your tank fallow for 72 days now if you want to be sure ich is not in your tank...


New member
Thanks for the reply.

It sounds like I could turn off the skimmer and remove the carbon. Treat the entire tank, with fish and inverts with a natural ich treatment and prazipro?

From what I understand, my temperature is also too high. I had my heater set to 80, and an analog thermometer that read 80. I hooked up a heater controller and averaged out two more thermometers and found it was more than likely actually 81 degrees.

My plan is to run it at 76. I was planning on using the controller to drop 0.5 degrees every 6-8 hours until I get there. (No more than 2 degrees, per 24 hours).


New member
Well, the problem with treating in the DT is live rock, live sand, and inverts - if treating with copper that is. Also, your DT will still have ich in the tank unless it is fishless for those 72 days (inverts can stay in DT) Three proven methods to treat ich are:
1. tank transfer method
2. copper
3. hyposalinity

See: http://www.reefcentral.com/forums/showthread.php?t=1992196 thread for detailed info about ich.

Both copper and hyposalinity will cause issues in your DT by killing inverts and live rock. The LR may also leach copper later on in to the display tank which could create a nightmare, including, but not limited to: invert death, below par water parameters, etc. Obviously, the TTM is impossible in your display tank.

At first, I really did not want to QT, as I live in a small apartment and space comes at a premium. But, after making that mistake (that is - being to impatient to quarantine) I realized how depressing leaving my DT fallow for 72 days was plus where to store my multiple fish. At least if you QT, you are not treating all of your fish at once.

Also, after looking over your water parameters again, I would suggest using a buffer to raise PH to 8.1-8.4 (8 is a touch too low). Also, you should put some phosban or other phosphate remover in your filter or sump to remove some of those phosphates. As, for the temperature, I think 76 would be good. With my tank I use 3 radion LED lights that produce some heat, the way my DT is setup (i.e. since I need a cover on it because I have cats who would just love to have some sushi), my tank temperature fluctuates throughout the day (+/- 1 or 2 degrees) which is not ideal. If you can manage to keep your temperature stable at 76, I think that would be a good move. I know clownfish require between 72-78 degrees (not sure about your tang, but it is likely the same range).

Prazipro will treat for internal parasites. While some have used it in their DT, I have not so I cannot comment on what effects it may have on your DT.

Long story short, I would:
1. Give in to the fact you will need to separate the fish from the DT (I know it's hard but it's worth it in the end - trust me - you can read previous posts of mine where I am trying to wriggle out of QT-ing or treating ich in some other way, but the reality is that it's just not worth it)
2. Lower temperature as you stated
3. Remove phosphates
4. Treat fish in separate QT (even a cheap rubbermaid with circulation using one of the methods above)
5. Leave DT fishless for 72 days

I know it's hard now, but in the end, you will see that QT-ing is much less of a hassle than treating the DT or losing livestock :)