I’ve had three (of 10) swordtails die off in a community tank over the last week or so.
Water params are decent, per my API tests:
ammonia - 0
nitrites - 0
nitrate - 20
ph - 7.6
high-range Ph - 7.4
It’s a 75 gallon, with FX4 canister filter (which is rated for bigger tanks.)
Temp: 78-80
I got 10 about a month ago. They were in with one Angelfish, four glo tetras, six corey cats and one bristlenose plecos, so understocked.
I noticed some swordtails hiding in plants, others on bottom of tank. One died, and I suspected the angelfish of bullying, so moved it out. They still seemed to be hiding, then another died. Now the glo tetras can get nippy, too, so I moved them to another tank. Today, with just the swordtails and corey, I found another dead one.
Of my survivors, four at the top of the tank (no longer hiding in corners), but three are just sitting on the bottom, kind of hiding. Since the others died, I’m assuming this might be illness (rather than birthing fry.)
No other species have died or shown any illness, lethargy.
Any idea what’s wrong? Or how I can figure out?