What would that phytosanitary mixture be about in the culture media? Is there a topic in the forum where it is explained?

It may have been discussed somewhere on here before but I haven't looked. It's a media addendum that helps prevent contamination by fungi and bacteria and can also be used to surface sterilize seeds and explants if the typical protocols using bleach, etc. aren't working. A little bit goes a long way. Here's the website, check the product description and FAQs. Plant Preservative Mixture (PPM) 30 Milliliters

I have used this method with Oeceoclades, Eulophia, Cynorkis, Ansellia species and Cattleya hybrids. I am so glad I found this.