At the time I sold the black spirits I had no bronze fodder. I think I was collecting silver & platinum units from event and combining the plat w/ 3 plat spirits each. Needed all the room for them and didn't have barracks expansions, probably around 170 slots. No room for 20 fairies I wouldn't need in he foreseeable future

Of course now I will need more than I have saved up and can only farm spirit X