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Puzzling Black Skirt Tetra Forehead Spot


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Hello everyone,


New to the forum, and getting back into fish keeping and planted aquariums after ~20 years off.


I’m seeing something with some Glofish tetras (black skirt tetras) that I haven’t seen before and can’t find anything online about other than one or two other people having it.


I’ve had three from a local fish store exhibit an orange “forehead” or between the eyes. After some initial stressed behavior they have acclimated to the tank and seem happy and healthy (though I have wondered about too small a number, hence this next part about getting more to build more of a school). I chalked the strange discoloration up to unknown but harmless reasons. See the attached picture, the orange spot is most pronounced with the light blue fish coloration.


I recently bought some more from the local Petco. They weren’t in the best of shape to start out (bellies seemed a bit sunken, all were small), but I figured it would be fine. All three died in the quarantine tank within days of coming home, and had the between the eyes orange coloration show up. But it was also much worse, and seemed more like bruising or red discoloration as well.


I have been speculating and researching as to possible causes, and want some of your ideas.


I don’t expect that a disease would act that quickly, but who knows?


I wonder if it could be shock because of high pH or GH. I have pretty hard water and have been working to bring it down by using distilled whenever I change water, and just noticed that some reference sites show black skirt tetras as preferring a somewhat acidic pH. I didn’t think to test the water from the fish store before mixing in some as part of the acclimation process, so perhaps the swing was too great?


I have pictures of the dead fish for comparison as well, but leaving it off for now. Other fish were added at the same time as the initial tetras, and none of them have any of the same symptoms. Some worked through some ick; interestingly the tetras were the only ones never showing any signs of ick. All are happy now.


Water parameters:

temp: 76 F

pH: ~8.2-8.4, now down to 7.8-8

GH: 180 ppm, now down to 120

KH: 150 ppm, now down to 80

ammonia, nitrite: 0

nitrate: ~20 ppm


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Now I’m wondering if it could have been ammonia poisoning, and perhaps the toxicity was worsened by the higher pH I mentioned? The stock rate was high in the petco tank (who knows how much ammonia there?), the fish were in the bag for a number of hours (though nothing like they would be if shipped), the bag water was dumped into the quarantine 10 gallon tank, and I didn’t add any stress guard to the bags or ammonia detoxifier like prime immediately to the tank after they were added. (I do use prime whenever changing water if using tap water).

This post is how I’ll do things in the future: 


Perhaps black skirt tetras are most vulnerable to ammonia toxicity at that part of their bodies, and after initial damage heals if the fish survive the orange coloration is like a scar?

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It could be a combination of things your pH is high for skirt tetras typically you would want a pH below 7.5  the death could have been caused  poor water quality at the store there water parameters could be a lot different from your causing osmotic shock or it could be a parasitic infection with the sunken belly you mentioned am not that familiar with glow Tetra's to no if the orange head is normal or  not @boogehmah

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