I do same as you and go by eye. With MC you wouldn’t think you’d need Cal Mag especially when your water is loaded with calcium already like mine- but sure enough. Under the LEDs for some reason it’s generally the first problem that pops up for me. In my outdoor garden with regular veggies (especially zucchini) it was a huge problem for a few years. Potassium silicate doesn’t seem to fix it for me.there's a couple growers here who do something similar. also seen growers elsewhere mention it plays nicer with some silica.
there's a few things about MC that i always found questionable. but it's performed well enough i adapted, and the ease of use can't be beat.
Funny enough I didn’t have much luck using geoflora indoors but I incorporated it into my veg garden this year (cause I had a few bags laying around) and had the best crops of veggies ever with hardly any blossom rot and no added Ca.