Angel Fish With Sore/ulcer?

[Prey]

Request Help (please!)

Tank size: 260l
pH: 7.2
ammonia: 0
nitrite: 0
nitrate: 25
kH: cant remember im afraid! - middle of the road on my test kit norms
gH: cant remember im afraid! - middle of the road on my test kit norms
tank temp: 27

Fish Symptoms (include full description including lesion, color, location, fish behavior): fish behaving normally, no signs of stress etc - it has what looks like a very clean ulcer just under its gill (sorry for poor pics). The edges of the area are very clean, not jagged or furry and the scales/skin are just missing - plain pink underneath exposed. Im worried about what this is of course but also if it is likely to affect the entire tank - unfortunately the fish were only bought yesterday from a trusted lfs (bought all my other fish and plants from there) and I didnt notice the sore until the fish were in my tank (still bagged) but the lfs had shut so no option but to release them...! They came from a healthy looking tank which i didnt notice any unhealthy fish in. I have rung the place and they will exchange the fish no problems - basically what is it? should I take the fish back? should I treat it? will i need to treat the whole tank even if i take the fish back? etc etc - any help very greatly appreciated!

Volume and Frequency of water changes: weekly, 20-40%

Chemical Additives or Media in your tank: standard juwel filter (6 stage sponge panels), add plant food and fert tabs, water conditioner of course

Tank inhabitants:2 angels, 4 corys, 4 barbs, 4 platys, 3 dwarf gouramis, 1 red tailed black shark

Recent additions to your tank (living or decoration):several new plants, two new angels (including this one)

Exposure to chemicals:none

Digital photo (include if possible):

 

[Prey]

Any help on this greatly appreciated - the fish in question has been exchanged by the lfs but do I still need to treat the tank for anything? Help!

 

[WILDER]

Ulcers are pink or red with a circling of dead skin around the edges.
You will need to treat with a bacterial med.
Keep any eye on signs of flicking and rubbing, as ulcers can be caused by parasites.

 

[Prey]

Thanks for the reply - the area is pink exposed flesh but no soreness/dead skin etc. I exchanged the fish last night and was told it was a gill defect and therefore not to worry about treating the tank for anything - however if anyone thinks otherwise I may still do as I really dont want any problems with other fish.

 

[WILDER]

Bless him.
With gills defects as long as water quality is kept to its best there no problem.
He was a little cutie shame.