# Trimming the first 5 low(er) quality bases from forward and reverse reads results in 25% more sequences removed as chimeras

**URL:** https://forum.qiime2.org/t/trimming-the-first-5-low-er-quality-bases-from-forward-and-reverse-reads-results-in-25-more-sequences-removed-as-chimeras/13768
**Category:** User Support
**Created:** [February 25, 2020, 7:54pm UTC](https://forum.qiime2.org/t/trimming-the-first-5-low-er-quality-bases-from-forward-and-reverse-reads-results-in-25-more-sequences-removed-as-chimeras/13768 "2020-02-25T19:54:36Z")
**Posts on this page:** 1
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### Author: ![Nicholas\_Bokulich](https://forum.qiime2.org/user_avatar/forum.qiime2.org/nicholas_bokulich/32/19937_2.png) [@Nicholas\_Bokulich](https://forum.qiime2.org/u/Nicholas_Bokulich)
#### Post date: [February 26, 2020, 7:03pm UTC](https://forum.qiime2.org/t/trimming-the-first-5-low-er-quality-bases-from-forward-and-reverse-reads-results-in-25-more-sequences-removed-as-chimeras/13768/2 "2020-02-26T19:03:47Z")

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Hi @ngarcia,  
Are primers trimmed from these reads? This can often lead to unexpected chimera filtering, e.g., see this topic:

> [@Low sequence retain after DADA2 step](https://forum.qiime2.org/t/low-sequence-retain-after-dada2-step/13699):
>
> Hi! i know this has been asked lots of times, but i'm getting very low sequences after DADA2. This seqs correspond to V3-V4 region (expected amplicon size ~460) I tried triming F- 280 and R- 220 and without trim, but i lost A LOT in both, any advice? or help? [fulldenoising-stats.qzv](https://forum.qiime2.org/uploads/short-url/xtOib4OdGO8dJ8auylKU780ujbq.qzv) (1.2 MB) Denoising stats for NO trimmed. [shortdenoising-stats.qzv](https://forum.qiime2.org/uploads/short-url/801DeFo7e2G4lkbn8whVNIGQ42N.qzv) (1.2 MB) Denoising stats for trimmed [palmsequences.qzv](https://forum.qiime2.org/uploads/short-url/5Nz6co8Vr0eMrfrGWLrCbb0dM8R.qzv) (290.7 KB) sequences it self.

You could also try adjusting the `min-fold-parent-over-abundance` parameter, there has been some interesting discussion on the forum regarding how and when to adjust this parameter, could be worth taking a look: [Search results for 'min-fold-parent-over-abundance' - QIIME 2 Forum](https://forum.qiime2.org/search?q=min-fold-parent-over-abundance)

Good luck!

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