Just used this black sealer for light leaky seams and pinholes. Spraying in the dark doesn't work well for my aim. Used my green inspection light for better aim. Could be used with drywall mesh to reinforce. Otherwise works great.
Thanks for the offer but I think it's just an outlier. If I get more stunted plants I'll start looking into it more. All the rest of my plants are going great in the same environment.