Not sure about the BC boost, I have not used it. With that low a water you are lucky and yes you need the calmag plus. Or maybr you don't need the calmag ?

Technaflora introduces a way to have a superior hydroponics crop in two simple steps. Use B.C. Grow (1-3-6), B.C. Boost (3-0-2), and B.C. Bloom (1-4-7) in the tested and proven mixing ratios printed on every label for optimal growth and maximum yield. Unlike some other three-part nutrients, B.C. Nutrients are easy to mix and control because you use just two parts (Grow and Boost or Bloom and Boost) during any growth stage.

Both Grow and Bloom are fully balanced formulas containing all the essential elements and micronutrients, while Boost contains mineral supplements to boost plant development in any stage. B.C. formulas are pH balanced, reducing need for pH adjustments. With B.C. Hydroponics Nutrients there are no secrets, and no guessing!

Might check some out next time around.