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Discussion Starter · #1 ·
New to aquariums. I recently got neon tetras, 9, of them to a 20-gallon long tank. Water tested perfectly. One male tetra seems to be territorial guarding half of my tank and not letting any other tetras come near it. He does not school with the rest of them. After feeding them today, I saw that other tetras were chasing each other and nipping. I also have a cardinal tetra in the mix who has a white patch on him, not a spot like ich, but I am not sure what it is. My other neon tetra just has one small ich looking spot. Any advice?


tetra disease?

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You may have a bad mix of males to females in the group and just need to get a few more to balance it out. They are difficult to sex- but, getting 3-5 more should give you a better balance.
With neon's, it is most likely a male or female that is ready to spawn who is keeping others away. They do not display this territorial behavior 24/7- only during times of spawning activity.
I cannot see the photos clearly enough to tell if Ich on tail. One spot does not make Ich, however. Ich is very distinctive, you will see white spots like sand covering parts or all of the fish. Its hard to mistake once you see it. I would have a bottle of Paraguard ( or other anti-parasite medication containing malachite green) on hand just in case. If you identify Ich, you must move fast to treat it.
But, this area of whiteness is most likely from netting, transport, etc... when got the fish. Many times fish will get these surface scrapes, damaged scales, etc... and will become infected with bacteria. Clean water and good nutrition should take care of it. But, if you see fungal growth or fish becomes lethargic or wont eat you will need to take different measures.
Why do you have only one cardinal? Did you lose some others? Or did I misunderstand and you have more? Cardinals are immune to neon tetra disease , so what it has would not be this. I am a bit concerned by the photo because the area of whiteness appears to be in the dorsal area which is often associated with Columnaris disease or "saddle-back" disease. But, I cant be sure because the photo is too blurry.
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