Tiger barb die off.

[Tazie]

Ive had a small schoal of tiger barbs in my 20gal tank. I had six of them for almost a year and just got 3 new babies to join thgroup a few weeks ago. So i had a total of nine. Yester day they were all swimming normal chasing each other around the tank like they normally do. Today when i got home from work 6 of them were dead.
I checked the water with a liquid test kit and everything was basically the same. Just a little bit higher from all the dead fish sitting in the tank all day.
I also have a small schoal of khuli loaches in the tank and they are all fine so i dont think there was a spike in anything since theyre a more sensitive fish. Any ideas on what could have killed off my tiger barbs within 24 hrs with no warning. Thank you

[Andy Sager]

Barbs in general are very sensitive to water parameters. 6 in a 20 gallon tank was pushing it and then adding 3 more was really pushing it. If you noticed their gills flared at all when you found them, that's a sign of lack of oxygen or water conditions going bad. If they died with their gill plates closed, that's a sign of a natural death. When you have 6 fish die at the same time, that's a sign of water issues. The fact that you did tests and they were " basically the same" says to me that it wasn't okay at some point and what the Barbs contributed to it not being okay was remedied by your biological filter or your filter that re-oxygenated the water. You would need to supply more specifics as to which fish died, the length of time from the addition of the new fish and your specific set up and water values before and after the additional fish and post deaths to make a more concise diagnosis.

[ColdKoi]

What are the water parameters? What kind of setup do you have (20g long/tall/ect, filter, air stone?)

9 barbs and a handful of khuli loaches would be a decent bio load for a 20g tank.

What type of test kit are you using? I’ve had an older (but still almost a year from expiring) api kit start giving me false negative readings. Bought a new kit and side by side compared them and the new kit was giving me the expected readings (tank has been stable for years)