My wife is a member of a diaper science community on facebook group called fluff love. They have extensive information about how to get your diapers really clean, with targeted information for specific situations like water hardness, washing machine type, materials, etc. The folks there are very helpful and responsive to issues.

What we ended up doing was 1 "power wash" cycle, followed by a regular wash cycle each time, and just regular ol Tide detergent. Sorry for the tide ad.

Short answer: it's hard to say specifically, because it depends on a ton of factors.