Question ... do you dilute the VCT for application or not ?
The only way is to test it and the easiest way to do that is use radish seedlings. Sow some in straight perlite or with some vermiculite and they will germinate in a few days. When they have a reasonable root system - about a week - you can test your brew. Take them out of the pot when you are ready and check the root tips with a hand lens. If they are white and clean with no brown tips your mix is safe to use. You can then experiment with concentrations.My problem is one of trusting my brew.