I used the Red Bag which holds 2 Cubic feet in each bag from Home Depot. Its the only Pro Mix they carry.
PRO-MIX 2 cu. ft. Premium Moisture Potting Mix Compressed Soil 0306RG - The Home Depot
Growing beautiful, healthy plants is every gardener's goal. Make sure you achieve the best possible results with PRO-MIX Moisture Potting Mix, a high-quality, ready-to-use blend containing sphagnum peatwww.homedepot.com
that's totally the wrong product for cannabis. you want to use promix hp. it's understandable you would have issues. that mix can have issues when using nutes.
edit : that mix might not be ph balanced either. they balance the hp for use with nutes.
more edit : i'm not convinced that cal-mag is the best.