It is not recommended to mix silica with your nutrients directly. I’m not sure about the Lucas Formula in particular but I imagine it’s like any other additive, where, as @Growernick stated, it will form a precipitate with Ca/Mg and can react with other compounds as well. This is one of the reasons SI is not normally incorporated into hydroponic nutrients already, despite its beneficial impact on plant health.
Another thing to note is that if you will be adding SI to your water, it’s always recommended to add it before anything else, once it has been well diluted in the water.
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