The Puffer Forum

I set up a reef tank about 3 months ago, where I added in my first few fish about 4 weeks ago. One of them is a Ostracion cubicus named puffy.

When I got him in, he was looking healthy, but over time (about 1-2 weeks ago) I started noticing some white spots (but only with certain light). I suspect ich... However none of the other fish seem to have any white spots, and the spots only show on his fins, just like is described in this thread: viewtopic.php?t=18130
In addition, the fish eats fine and swims around happily, not scratching or anything

I made some photos / short video's to show you what I mean:
https://www.dropbox.com/s/37oa3uvyqnf0u ... 9.MOV?dl=0
https://www.dropbox.com/s/9mwzefo0kegwv ... 0.MOV?dl=0
https://www.dropbox.com/s/ku1455w1g9d5n ... l.png?dl=0

What would it be and what can/should I do about it?

Finally, my water params are:
25 degrees celcius
1.025 salinity
0 NH4
0 NO2
<0.5 NO3
7.1 KH
8.15 PH
and the other fish in the tank are 2 Snowflake clowns (amphiprion ocellaris Snowflake), and 1 Blennius (Salarias fasciatus)

As stated in the thread you linked to & another linked there, these "marks" are just irritations (think light bruises) that are nothing to worry about. They come & go.
Just a warning, as far as your boxfish species--if this fish gets stressed at all, it can emit toxins that can wipe out your entire tank, including corals. Also, I would not consider them to be reef-safe.

Thank you for the comforting words on the marks. The warning you stated makes me question the professionality of the LFS that sold me this fish, as they stated it shouldn't be a problem, even though they are aware of my tank's inhabitants and I asked them specifically.

Should the fish not be held in tanks at all given their toxins, or are there measures to prevent them from whiping out a tank in case of stress, such as filtering over active carbon?

Absolutely, I suggest using Purigen to help prevent chemical warfare between corals & possible toxin release of this fish. I like this product, because it is rechargable.
Yes, LFS's job is to sell you fish. It's our responsibility to do research on them. Also, are you aware of their adult size?

Ah Purigen, I run that in my fresh water cichlid tank to reduce nitrates Should have some spare, which I will put in asap. I am aware of the adult size, and also discussed that with the LFS owner, on which he said it would be no issue to trade it out once it becomes too large for my tank, which might not even happen because I expect to upgrade to a much larger system soon

I find LFS' are notorious for intentionally not giving needed info to ensure a sale. When I first got into saltwater tanks, I went to a fish store called Valencia Pet. They sent me home with enough saltwater to fill my 24g Nano Cube, a flowerpot coral, a Anemone, 2 Percula Clowns, a goby of some sort, and a Cowfish (still my favorite fish and will be a main point of the 240g tank I am saving for). I think one of the most important things to note here is that they sent me home with this stuff knowing I had not cycled my tank (didn't even fully know what cycling was). No surprise, everything died fairly quickly. Not only was that just plain bad customer service, it was unethical and immoral. They knew these fish would suffer and die and they did it anyway. I take very little stock in what a LFS says.

OMG!!!

That's just insane!