Urgent - What is this??

[pdoutaz]

I have 7 Columbian Jewel Tetras in my 120G community tank - about 2 days ago I noticed discoloration on 1, has now spread to a second one. All other fish / species seem to be fine.
Only recent change - started CO2 about 3 weeks ago - closely monitored, PH is about 6.8 - 7.0
Sorry for the poor pics, but hopefully shows enough to see the problem.
Thanks

[clintgv]

I don't see any pictures?
Did you forget to put it up? ^^

[Claudia]

I dont see the pics anywhere

[pdoutaz]

Don't I feel foolish - Pics added

[pdoutaz]

Anybody know??

[Adz1]

Don't I feel foolish - Pics added

are you asking about the dark spots?

[pdoutaz]

Yes. the pics don't show it well, but the dark areas are almost black, seem to be increasing in size also....

[Luke78]

Have you had the chance to run a few tests on the water? introduced any new stock or plants without quaranting them? Having their colour change to that could be water related.Reason i say that is , ammonia burns leave these kind of marks or discolouration.Seen it happen to a few goldfish setups(huge ammonia producers) when their water wasnt changed.I would also closely look at your filtration and make sure the media is clean, or needs to be changed.

[pdoutaz]

Thanks Luke78 - I am going to pick up a new Test Kit tomorrow - current one is too old (about 2+ years) except for the PH tester which is new, so I don't completely trust it. Media was cleaned / changed about 10 days ago - on both the 2 AC110's and the XP4, water was also 30% changed at the same time, so I don't think it ammonia, but will certainly check tomorrow? Nothing new added to tank in last 60 days, except I started CO2 about 3 weeks ago.

ANY other possible causes come to mind?

[pdoutaz]

Water tests negative for ammonia - anyone have any idea what the cause is???