How did mycorrhizae get in the res? Did you put it there? It's not the kind of thing that floats around in air looking for a RDC to live in.
If you are taking tap water direct into the bucket, that is a harsh environment to start in anyhow. The stuff they put in municipal water is designed to kill any microscopic life.
I agree you could do nothing and finish the grow, but next time you will need a plan to prevent root issues.
This is where the internet can actually hurt you - you are getting into the area of opinions and you really don't know who to believe. Ask yourself this - if using water from the tap and not adding anything but hydroguard
(contains no mycorrhizae) - what are the chances you have a colony of them? IMO approaching zero. I still don't see it in your pics either.
This is what a colony looks like
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