Originally Posted by John0216
How long did you have the tetra before this dying began? 5 days
When you say the pH is high, what is the actual number? And for comparison, what is the pH of your tap water? Do you have a pH test kit, or relying solely on the store tests? Relying on store
Are you doing regular water changes, and if so, how often and how much of the tank volume?Yes, every weekend, 10%
What is the temperature of the tank water? 78
When was the tank set up? 3 Weeks ago.
What fish (species and numbers) are now in it? You could look at my aquarium log. That would be easiest (55G Family Tank)
This problem may have originated with the tetra themselves. I have had internal protozoan (which cannot be detected externally, and only become evident when the fish begin dying) manifest themselves after 5-7 days. It would seem less likely that a protozoan introduced with the newest fish (the DragonFish) would begin decimating the tetra in a day, and not affect any of the other fish.
You will need to be very careful now. Not knowing what this is, means it is useless to attempt treating for whatever it might be. Medications are stressful on fish, and using one that is not specific to the issue will only add to present stress and make things even worse. On no account add new fish to this tank. Increase the water change to 1/3 or better yet 1/2 the tank volume once every week. Use a good water conditioner, but add no other substances. Feed the fish once daily, but do not overfeed.
Keep us posted on fish deaths, if any more occur, and which fish species. If you can get a clear photo of any fish with the white patch, this might help.
On the pH and the store's comment, without the number we can't say much. It would be a good investment for you to get a liquid test kit, and while you're at it, the API Master Combo is well worth it. This kit has tests for pH, ammonia, nitrite and nitrate; these are the basics you need especially when there may be a fish health issue. The liquid test is better, much more reliable, than the test strips.
Keep us posted on developments. For the future, you need to increase some of the fish species you now have [I saw the log data]. Kuhli loach should have 4-5 minimum; and all tetras are better with no less than six and preferably more. The Black Phantom Tetra should be around 9 [you have the space in a 55g], and a mix of male/female is good; the profile explains how to tell them apart [click the shaded name for the profile]. The "von Rio" tetra is probably the Flame Tetra, and this too would be better with 7+ but wait until things settle down before getting any more fish.
Is it feasible for you to have a small Quarantine tank? A 10g is fine for this. Once you have a 55g established with healthy fish, the last thing you want is to lose most of them with some protozoan. I speak from sad experience.