I think Mark uses Chem Gro but Masterblend should be about equal and it's cheaper.
https://hydro-gardens.com/product/to...s-bag-4-18-38/ $58 for 25 lbs
https://www.morgancountyseeds.com/pr...lizer-4-18-38/ $37 for 25 lbs
Buying it 25lbs at a time is the way to go, I bought MB 3 years ago and still have about 10-12 lbs left but I've only used it in dutch buckets.