its hapened to me ,its the miricle grow ,this soil give loads of nutes probs as itcontains its own on slow release and with you feeding on top the plant gets used to the nutes from the mg soil and your canna terra nutes and when the soil runs out of nutes, usualy about 3rd month and you stop given the canna terra the plant goes into severe withdrawl for a week or 2 turning the buds rusty dont flush her to much and she will be ok but the buds will stay rusty but fine ,
hope this is any use when i experianced this i ditched the mg after that done my brain in but ok for first grow learning process at leasdt you now know its a nono