There is your problem, MiracleGro. MG is bad for Cannabis and really any plant. MiracleGro contains Copper Sulfate a toxic pesticide. But the biggest issue with MiracleGro when growing Cannabis… NITROGEN. Plus your using Cal/Mag w/ 3-0-0 which means your adding even more Nitrogen when you fed the Cal/Mag.
MiracleGro uses time-release fertilizer. This means its constantly releasing Nitrogen. Might do you good during veg but come flower plants dont use as much Nitrogen as they would in veg. This leads to toxicity. Overall the brand is toxic, the nutrient forms are toxic. Urea nitrogen and ammonium sulfate create harmful greenhouse gases when exposed to the air which can damage human lungs.
If I were you, Id avoid any MiracleGro products whatsoever. You would be doing you and your plants a favor. Your plant is already been flowering with the toxicity so flush all you want wont fix it. And if your ysing MG soil you definitely wont stop it by flushing it simply wont happen unfortunately.