I know, that sounds terrible. But I got my shipment of RCS's yesterday, and I was oh so excited drip-acclimating them for the tank. Which went fine. It all went horribly wrong when there was an issue and I had to do a 100% water change just an hour or two after they got put in. (An issue with my husband not knowing if he could put something that had been washed in the washer in the tank... He's not the Betta Keeper of the house. I've banned him from the aquarium.)
But I did the water change and reintroduced them to the tank. I looked this morning, and they are all in fact not living anymore. I had done a test yesterday before I put them in:
Nitrate: 0-15
Nitrite: 0-.5
Total Hardness: 10-20
Alkalinity: 100???
pH: 5.5-6.5
I don't know if it was for worse or for "betta" (Sorry for fish-stick in a serious thread.. Oooh I'm on fire.

) But Niklaus' shipment was postponed until the 21st, so I wont see him probably until the 23-24th.
Please let me know what I'm doing wrong, and how to fix it. I feel so terrible that they didn't make it. My tank:
Inside:
-Black gravel sand
-Treated rocks
-Java Moss on Junglevine
-Bacopa
-Wisteria
-Anacharis
-Marimo Moss
-Filter (covered for Shrimp, will probably now be uncovered)
-Heater
-Betta Hammock