[Guy Rabens]

Hi All,

I am new to the Saltwater Aquarium hobby. I have a Yellow Tang I have had for about 3 months. He has gradually gotten a reddish brown patch near the tail on both sides within the last week. I talked to my local aquarium store but have not gotten much information other than to keep an eye on it. My tank water checked out ok. The Tang is swimming, eating, and generally acting normal other than the patch of skin discoloration. My other fish in the tank do not appear to have similar skin discoloration. Can anyone provide some information on what this might be?

Thanks in advance,


Guy

[leebca]

WELCOME TO REEFLAND!

Tangs in general have a relatively poor mucous coating. That is, their skin is more exposed to water quality and water conditions. Not all the things you test for tells you everything about water quality. Read through this post for more information about this: What is Water Quality.

There are things to ask about your system that you didn't present. If you want more help with this and you are not able to show us a photo, then you need to answer the following questions:
How old is your tank? When did it originally cycle?
What is the size (dimensions and gallonage) of your aquarium? Does the gallonage include the volume from the sump and any refugium?
Do you use carbon, skimmer, mechanical or other chemical filtration?.
List all specimens & sizes in the tank (fish, inverts, corals, clams, snails, crabs, shrimp, etc.).
Do you use a quarantine tank and procedure?
Foods you use and feeding schedules.
How long have you had this fish? If the fish was recently acquired (6 weeks or less), two more questions: Did you treat it or give it a dip before it went into the aquarium? How did you acclimate it – what procedure?
Do you use any vitamins? Fat additives? Any elemental or other additives? Please list all.
Chemistries – you gave some indications but not actual numbers. Do you test for Phosphate, alkalinity, calcium and magnesium? Please give actual current numbers for everything. Have these numbers been changing lately?
Water parameters – please give actual numbers (pH and your pH range, salinity or sp. gr. & range, temperature range)
Do you see any of the following in your system: hair algae; micro algae; cyanobacteria growths (red slime algae); dinoflagellate (zooxanthellae) growths; brown algae; diatom growth; slimes; off-colored patches on rock or substrate that are not coralline; etc.?
Water changes (how much and how often).
What is your source water? (Tap water, RO water, DI water, RO/DI, distilled, etc.)
List what you added or taken out of your aquarium system (living, decorations, and equipment) during the past 6 weeks.
Maintenance schedule. What have you done lately?