The picture I attached is some nutrient samples I got from my local grow shop would this work as a replacement for the cal mag?
Does the bag say anything about what its content is? (Guaranteed analysis? Whether it's carbonates, sulfate, chloride, nitrate?). The only thing I saw on their web site is that it's 12-2-12 (with 6% Ca, 3% Mg).
Botanicare Cal-Mag+ is 2-0-0 (3.2% Ca, 1.2% Mg). If you fed enough of that sample to get the same Ca & Mg, you'll be feeding substantial amounts of N, P & K.
It could be good stuff. But, if you follow a schedule for GH Flora 3-part, you'll be altering its NPK ratio considerably. IMO, that's more of a fertilizer product than a "calmag".
I can't stress enough: the best thing to do (first grow) is follow what someone does. If you start using different things because you have a good feeling about... that's how new growers get into trouble. Follow a known gold-standard, and then experiment with things. You'll have a baseline to compare against.
It's possible that nutrient seller created that "calmag" product to work with their "system." Their base nutrients may depend on that 12-2-12 to arrive at a planned NPK ratio. Honestly, I would stay away from boutique products like that. Cannabis doesn't need special nutrients. Much of the cannabis-themed products are overly expensive. You're paying for the resulting NPK ratio (which you can create yourself). Their often designed to work together as a system (and lock you into that "lineup") because all you know is "5ml of the cross-eyed giraffe, 2ml of Einstein picking his nose, and 8ml of smiling monkey produce really good results." All the plant sees is NPK ratio and strength. Those cannabis-themed "lineups" obscure that less subjective information. It becomes an all-or-nothing proposition. The amount of NPK that "calmag" product has tells me, it may be part of a "lineup" that way, and may not work well by itself.
I'm just saying, if you use one "lineup" product that way, oddball stuff... you could stumble onto something very useful. Or, you could cause yourself problems. It's probably going to be a flip of a coin which way that goes (unless you vary the GH Flora 3-part schedule to accommodate this "calmag's" unusual NPK level). I just think for a first grow, it's a no brainer: Stay within the lines. Follow *exactly* what someone does. Develop a baseline to compare to (when you start experimenting, learning to read your plants, etc.). Playing around with odd stuff like this is inviting problems.