If 75 degrees is too hot for those, you shouldn't keep them with a betta because my minimum for bettas is 76.
You can mix it, I'm not sure if it will transfer as I'm unexperienced with cycles. I don't think it would though since I believe it's in the filters too.
Milo : Crowntail, SIP;-;, Vivian : Crowntail SIP, Kawaii SIP, Kano : HMPK, Igneel : Halfmoon, Atlas : Feathertail EE, SIP, Magnus : DTHM, Avian : HMPK, Juno SIP-Delta,
Alias-HMDT ,Blu-Delta, Tanso : Wild Smaragdina,Neslet-HMRT, and Hetalia.
Calico-Shubunkin and Comet-Comet *DECEASED*