An update
My tank cycled quickly because I had all used rocks, a used bubble strip, one used rock ornament and about 1/2 gallon of used water when I set it up. It was a friend's tank for years and they got tired of it. It had a kissing gourami in it that I rehomed.
I bought the API master test kit. Water parameters at 1pm were:
Nitrates 15
Nitrites 0
Ammonia 0
PH 7.4
Temp 79 F.
So today my 6 swordtails were happy, swimming and eating. By 7pm my 2 female red velvet tuxedo swords were dead. One started doing erratic swimming and back flipping. The other laid on the bottom and died.
I quickly did a 25% water change, added stress coat water conditioner and bio boost. The remaining 4 seem ok. But idk what happened! ?!