I'm trying to QC my illumina miseq paired end reads with sickle pe. but, as visualized in Fastqc per tile sequence quality, it seems that I can not get rid of low quality sequences from special tiles (2118) but somehow it even get worse by increasing quality threshold.
this is the screen-shot from my reads per tile sequence quality after trimming with default quality threshold of sickle pe (q 20):
and this is what I get after increasing that to q=30:
any Idea about what happens around 2118?