It's been many years since I last contacted you and must say that I certainly appreciate your column in FAMA each month. I've gleaned a lot of information over the years and want to thank you for you're many efforts promoting saltwater systems and caring for our creatures.
I have a 150 gallon reef tank with a deep sand bed (but no plenum). The tank is doing well, however, I added a Hepatus Tang about 2 1/2 years. ago. He grew rapidly and is now about 8" long. He has developed some sort of skin ailment (after he was about a year old), similar to lateral line disease, yet not exactly the same. I'm attaching a picture of him after treating with Selcon (soaked into extra large Mysis which only he eats) for about 3 months. It is a little over 4 months now and there is only a slight improvement over how he was at 3 months of treatment. He has a frazzled tail also. He's healthy as an ox and eats everything in site. I give him (and 2 other tangs - yellow & purple) Romaine or dried Nori nearly every day. The other tangs are in excellent shape.
Usual water parameters for this tank are: Nitrate less than 5ppm, Specific Gravity 1.025, Alkalinity 3.5 meq/l, PO4 less than .25ppm and the temperature about 81°F.
Got any ideas? Maybe I need to treat him longer?
Thanks for your help,
PS: I'm using a Salifert test kit for PO4. It's very hard to tell exactly what the reading is. Is there a better PO4 test kit?
Thank you for the kind words about my FAMA column. As for your problem with the tang, this very situation was discussed in my latest book, which also discusses many other maladies and proper feeding. As for this particular malady, from what I see in your photo, it's clearly Head & Lateral Line Erosion (HLLE), and often begins/appears as a pitted area on the face and/or along the lateral line of the fish, the cause of which has generated much conjecture in the aquarium world. For example, some think it caused by dietary or vitamin deficiencies (I'm in that group), stray electrical current or free electromagnetic fields, exposure to heavy metals, protozoan organisms, poor water quality, stress, the use of activated carbon, certain medications, and even various viral and bacterial infections. Even the lack of 'direct' sunshine is considered a possible cause, as this malady is never seen in the wild!
Nevertheless, I've seen it cured in a friend's tank with the feeding of excess Caulerpa (C. prolifera and C. mexicana to be exact/that's important, as those are the only two species of Caulerpa that most marine fish find appetizing!) from one of my aquariums. This aquarist also fed small amounts of flake food, mostly Spirulina, about 10 - 15 times a day that were soaked in all-natural over-the-counter multi-baby vitamins. It took about a year to overcome, but the fish recovered fully. A fellow hobbyist in the UK also used this method to heal his large angelfish. Because of this hands-on experience I'm a great believer that dietary conditions are probably the root cause of this malady, and that secondary infections/infestations take hold once the tissue becomes pitted. When that happens, the overall situation becomes even more complicated to cure.
As to your PO4 level, it should be no higher than 0.015 mg/l, therefore yours is 'far' too high, and 'may be' contributing to the problem area. And even though I have used the Salifert kit, and recommend it, I always add that 'any' indication of phosphate when using said brand kit is an indicator that the time has arrived to change the phosphate removing media in your canister/reactor filter. I'm now using the Merck kit, which is a little more pricy than others, but find it quite accurate!
Hope this helps,