# Which controls should be used when sequencing low diversity libraries on a MiniSeq?

Illumina recommends adding PhiX at 1% to all sequencing runs as an internal control.\
For low-diversity libraries, spike in higher percentages of PhiX to add base diversity to the run. The percentage of PhiX to depends on the diversity of the library, and requires optimization.

* For low or imbalanced base diversity libraries, Illumina recommends spiking in 10-50% PhiX. It is best to start optimization at a higher percentage of PhiX spike in and reduce over subsequent runs to maximize data output and quality.

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| *For any feedback or questions regarding this article (Illumina Knowledge Article #7047), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000007047%20-%20Instrumentation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |


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