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Last night I had 5 tiger barbs and this morning I have 4. No sign of the 5th anywhere. I have a 55 gallon tank with some driftwood and 3 pieces for the fish to hide in. In the tank I have 1 feather fin cat and 2 striped Raphaels but these guys never bother anything and only come out at night to feed. We have well water and ammonia is at 0, nitrite is 0, nitrates are high at 80 ppm and ph is 8.5. The water is very hard, like liquid rock. Usually tests off the scales. I have 6 more freshwater tanks and 1 brackish tank. All these tanks have been running for over 10 yrs. and the only fish I have had problems with are the barbs...? Any ideas would be appreciated !!

While 8.5 isn't that far from the ph that most barbs like it is a bit high
http://fishprofiles.com/profiles/freshwater/Cyprinids/Puntius_tetrazona/
The hardness of the water and the high ph as well as the 80ppm of nitrates are all contributing factors to fish stress. Once one barb starts showing a weakness I would not put it past tiger barbs to attack and peck at the weaker one until it was dead. Between the tiger barbs and the rest of the fish in the tank they'd easily dispose of the remains before you had a chance to see.

I'd increase water changes, and or add some floating plants like hornwort which are great at sucking up nitrates to get those nitrates down. 80ppm is really too high.
When you're doing your water changes make sure you don't over vacuum the gravel. Only do a third of the tank worth of gravel at a time so you preserve your bacteria colonies. Just because it's an established tank doesn't mean it cant also have a mini cycle. And while barbs are hardy fish ones that are under stress (from high ph, hardness and nitrates) can easily be put under more stress from a mini cycle, even though your test results don't show it.

You might try adding more driftwood to help lower the PH, though with water that hard it isn't likely to move at all.


One other thing, how new are the barbs to the tank?


^_^