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I though corn was the best one, more rhizomorphic, not fluffy like others, I dont think I have contam in any of them

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yes it's the cornmeal that looked suspicious.
I guess those yellow spots are just cornmeal. I thought you filtered the mixture and was concerned about the spots.

I would try to filter it after boiling it with water and add the agar afterwards while it is is still hot. That should give you a clearer dish.
IMO the yellow spots distract too much and possible contaminations are more difficult to spot.

Anyway. Good work