JustaGuyanswered grow question 3 years ago I Think it is an nutrient iregulation wich will turn into nutrient lock/-burn, because of an bad Watering schedule wich will cause trouble with the roottips after a certain time of Waterin. The TopMax help out to make the earth alkali metals even more available at the same time, trough his humic acis and other natur basic acids. May even a bit of light stress with result with magensium def... But i think its a nturient iregulation how i called.... May take a look at mulders chart or on RQS Article aout nutrient burn and over fert.
After too much available Phosphorus who increases the demand of Magnesium.....somethink like that can happen too... But i really think that Trouble stand in relatione with your watering cycle.
Wish you and your ladys the best. Greetz JustaGuy.