My daughter's tiger barbs suddenly started dying off. Although my pH and hardness is high in my source water, they have seemed happy and active up until the past four days. My other parameters have been more or less textbook perfect.
Four days ago, the smallest tiger barb stopped swimming with the others and retreated to the corner of the tank, where he stayed all day, not even attempting to eat. His breathing seemed faster than usual. Other than that, I didn't notice any other symptoms. I checked my water parameters to be sure, everything still looked fine. The next morning he was dead, sitting on the bottom of the tank, very pale.
The rest of the barbs seemed to be behaving more or less normally. I removed the body immediately, checked my parameters again did a ~20% water change. I dropped the water level of the tank slightly to give the filter a bit more aggressive oxygenation. Everything seemed fine and I couldn't find any explanation for the first death.
Yesterday, a second barb started showing the same symptoms as the first, hiding in the corner of the tank, not eating, and breathing rapidly. About an hour ago, I found him dead, stuck to the filter intake. A third barb is now showing symptoms. I just triple-checked my parameters and everything still looks great. I expect to lose him(her?) too, and I'm at a loss for what to do.
Tank size: 20-gallon
Cycled: ~8 weeks ago
Occupants: Originally 5 tiger barbs, now 3, ~1 inch. Been in tank for 4 weeks. Purchased from PetSmart (I know, not my first choice either)
Live plants added ~3 weeks ago
Fluval AquaClear 30 HOB
Water Parameters from API Freshwater Master Test Kit with expiration in 2024
tank temp: 78F
Volume and Frequency of water changes: 10-15% weekly, normally. But I added a 20% change when I found the first death.
Chemical Additives or Media in your tank: Fluval Aqua Clear filter for 10-30 gallons, sponge+active charcoal+biomedia. All filter media agitated in dirty water removed during water changes before being reinserted. Never washed nor rinsed in water containing chlorine, etc.
Tank receives natural sunlight 2-3 hours per day, and a bright Nicrew white/blue LED
between 6 and 9 hours.
Tank inhabitants: Single species (Tiger Barbs)
Food: Tetramin Tropical Flakes, twice daily, very small amount, completely consumed within 1-2 minutes
Recent additions to your tank (living or decoration): Live plants ~three weeks ago
Exposure to chemicals: None
Photos + videos of both dead fish, as well as the third fish showing symptoms: