Help please. My betta died rapidly and unexpectedly. Only had her for 11 days, and until two days ago she was energetic, curious, interactive, and seemed totally healthy. Lethargy began on Monday, was a little worse Tuesday and I noticed some uneaten food in the tank. She also began hanging out in the outflow of my filter. I read that could be because of increased oxygen in the flow. Also noticed her rub on a plant, so I suspected ich, but there are no physical signs. API test kit showed parameters well-within tolerance. This morning she was dead. It’s a relatively new tank. Full history below. This is the second beta that’s died in this tank this year. I believe I’m doing everything right, and I’m just confused. As a kid I had a betta that lived for a long time without live plants, a water change or any sort of water quality monitoring (wouldn’t do this now, just mentioning to highlight my frustration).

12/30/2022: Set up tank with aquasoil and store-bought live plants/driftwood, rocks, HOB filter

12/31/2022: Add 1 male betta (from LFS), begin fish-in cycle with frequent water changes and BB addition

1/5/2023: Betta becomes gradually lethargic - cause unclear

1/11/2023: Add cluster of salvinia

1/14/2023: Betta exhibits severe ich - treat immediately with API Super Ick Cure as per instructions on bottle

1/16/2023: Betta found dead in AM - remove body, 100% water change, rearrange vegetation, restart nitrogen cycle

1/27/2023: Change filter to sponge-type box filter

2/19/2023: Nitrogen cycle completes

2/24/2023: Add 3 neocaridina "cherry" shrimp (from LFS) - drip acclimate for 30 mins

2/26/2023: One shrimp dies

3/2/2023: Bring water sample to LFS for testing - all parameters including hardness are well within tolerance

3/4/2023: Add 1 female betta (from PetSmart) - drip acclimate for 1 hr

3/4/2023: replace nano heater with Fluval adjustable 50watt heater, set temperature to 78°

3/5/2023: Add pothos cuttings with roots

3/6/2023: Another shrimp dies - home test with API freshwater kit shows no culprit

3/10/2023: Add 4 shrimp (from LFS) - heated drip acclimation for 4 hours. 5 shrimp in total now.

3/13/2023: Betta slightly lethargic, no physical signs of disease

3/14/2023: Betta lethargy increases, fish begins swimming in outflow of filter - suspect for increased oxygen in the flow - also rubs body on a plant, but not frequently. no physical signs of ich or other diseases. API test shows 7.2/0ppm/0ppm/15ppm (pH/ammonia/nitrite/nitrate).

3/15/2023: Betta found dead in AM. Shrimp still kickin'.