# SILVA 138.1 LSU reference HELP

**URL:** https://forum.qiime2.org/t/silva-138-1-lsu-reference-help/18671
**Category:** User Support
**Created:** [February 26, 2021, 8:10pm UTC](https://forum.qiime2.org/t/silva-138-1-lsu-reference-help/18671 "2021-02-26T20:10:58Z")
**Posts on this page:** 1
**Showing post:** 3

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### Author: ![SoilRotifer](https://forum.qiime2.org/user_avatar/forum.qiime2.org/soilrotifer/32/21071_2.png) [@SoilRotifer](https://forum.qiime2.org/u/SoilRotifer)
#### Post date: [March 1, 2021, 6:43pm UTC](https://forum.qiime2.org/t/silva-138-1-lsu-reference-help/18671/3 "2021-03-01T18:43:26Z")

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Hi @matthewbur,

> [@matthewbur](#):
>
> I downloaded “SILVA\_138.1\_LSURef\_NR99\_30\_06\_20\_opt.arb.gz” from the arb-silva website to use as the classifier for 18S protozoa data in qiime2 2019.10.

The arb file is not the correct file to use. That is for use within [arb](http://www.arb-home.de/). As @colinbrislawn suggests you can download the fasta, and other files directly. For this, I'd highly recommend using [RESCRIPt](https://forum.qiime2.org/t/processing-filtering-and-evaluating-the-silva-database-and-other-reference-sequence-data-with-rescript/15494) to download the files you need. _Note: due to some recent changes, you may need :qiime2: version `qiime2-2021.2`_.

You can follow the approach outlined in this thread:

> [@Weird Taxonomic classification 28S rRNA](https://forum.qiime2.org/t/weird-taxonomic-classification-28s-rrna/18469/7):
>
> I can't really say, it is largely dependent on the sequence lengths present within the SILVA database. You can also simply filter everything to the same length too via filter-seqs-length. Also, one option is to not filter based on length at all until after you've extracted your amplicon region first. That is, you may remove short "full-length" sequences which actually contain your complete amplicon region. We allude to this in the tutorial: As for your next question... The SILVA 138 LSU was…

-Cheers!  
-Mike

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