> For the complete documentation index, see [llms.txt](https://knowledge.illumina.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://knowledge.illumina.com/instrumentation/nextseq-1000-2000/instrumentation-nextseq-1000-2000-faq-list/000005583.md).
# Custom recipes for Illumina Stranded libraries on NextSeq 1000/2000
**Background**
Read 1 and Read 2 of Illumina Stranded mRNA Prep, Ligation and Illumina Stranded Total RNA Prep Ligation with Ribo-Zero Plus libraries begin with a "T" because of [how the adapters are added](https://www.illumina.com/content/dam/illumina/gcs/assembled-assets/marketing-literature/illumina-stranded-rna-t-overhang-tech-note-470-2020-010/illumina-stranded-rna-t-overhang-tech-note-470-2020-010.pdf). This "T" makes the first cycle of each read low diversity, which can cause cycle 1 (C1) or fiducial errors.
While this can be mitigated by adding PhiX (minimum of 5% is recommended), Illumina also provides custom recipes that make this first cycle dark to mitigate this. A dark sequencing cycle performs chemistry only and omits the imaging step of sequencing by synthesis chemistry.
Please note there is a "loss" of 2 cycles from the NextSeq 1000/2000 sequencing by synthesis (SBS) kit to accommodate these dark cycles, as no data is generated during dark cycles but reagents are still used.
**Sequencing Run Setup**
In **NextSeq 1000/2000 Control Software v1.3+**, these custom recipes are **built into the control software**. These recipes can be found under the file path:
`/usr/local/illumina/recipes/[ILMNStrandedTotalRNA or ILMNStrandedmRNA]/[LO or MO or HO or XO]/[v3 - v7]/recipe.xml`
**Table 1**: Sequencing Recipes available with Dark Cycles for Illumina Stranded mRNA or Illumina Stranded Total RNA libraries.
| | **Standard** | **Standard (600 cycle)** | **XLEAP** | **XLEAP (600 cycle)** |
| -- | ------------ | ------------------------ | ---------------------- | --------------------- |
| P1 | LO v3 | n/a | LO v6 (300 Cycle only) | n/a |
| P2 | MO v3 | n/a | MO v5 | n/a |
| P3 | HO v3 | n/a | HO v5 | n/a |
| P4 | n/a | n/a | XO v5 | n/a |
**IMPORTANT NOTE**: The P1 XLEAP 100 cycle kit and all 600 cycle kits do not have Dark Cycle recipes and require a minimum 5% PhiX spike in.
When selecting an Illumina Stranded library prep kit in sample sheet or in cloud mode, the NextSeq 1000/2000 control software automatically pulls the correct custom recipe; however, control software does **not** display a custom recipe is invoked. For the recipe to be automatically invoked, the sample sheet "LibraryPrepKits" field must say "ILMNStrandedTotalRNA" or "ILMNStrandedmRNA" only.
**Run Setup in Standalone mode**
Custom Recipes can also be selected when initiating a run in standalone mode on instrument. For instructions, see the "Initiate a Standalone Run" section in the [NextSeq 1000/2000 Product Documentation](https://support.illumina.com/downloads/nextseq-1000-2000-product-documentation-200027171.html). As previously stated, 2 cycles of SBS are consumed from the total number of cycles to sequence the dark cycles.
If additional assistance is needed, contact [Illumina Technical Support.](https://www.illumina.com/company/contact-us.html#/united-states/technical-support)
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| *For any feedback or questions regarding this article (Illumina Knowledge Article #5583), contact Illumina Technical Support* [*techsupport@illumina.com*](mailto:techsupport@illumina.com?subject=Question%2FFeedback%20Regarding%20Illumina%20Knowledge%20Article%20#000005583%20-%20Instrumentation%20\&body=Dear%20Illumina%20Technical%20Support,%0D%0A%0D%0A)*.* |
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