Hiya vostok, Think Hairy Haggis means this stuff?
Or The Stuff you get in the Bottle, Regardless HH read the Label and Half the amount it States(Don't give full dose) Ml > Ltr or whatever IF its powder then again Half what the company says to use, better to be Safe than Sorry.
Peace
EDIT: After wk or so, you can up the Concentration of MG per Ltr of water, or how ever the Stuff works.
When you re-pot give em good watering and then don't water unless Soil/Compost mix looks dry...easy to over water in the first few weeks
Little Tip after you re-pot and before you water-in...IF you can weigh the Pot/Plant Dry(Dry-ish) Kitchen Scales OR Bathroom(Depends on size n weight of *New Pot) then after watering-in and letting run-off drain..Weigh again..then you have a Dry n Wet(Watered) weight for future Ref.
Peace
Oops nearly forgot: If unsure when it comes to Watering after the First watering-in when to do..I tend to water every 3 days or so...But a Good Trick is to use your Little Finger at the Edge of Pot rim and insert into soil say about 1.5" if moist-ish Soil/perlite sticks to finger when removed give her another day before Watering.
Hope All goes well
I Don't use MG, But a fair few peeps do and have good results...
IF you Google MG in Cannabis, You will get loads of results, posts n forum Chat about peeps Who DO and Peeps Who DON'T use....
Different Strokes 4 Different Folks...
Me I use BioBizz GROW / BLOOM / ALG-A-MIC / HEAVEN and next I'm gonna try out Advanced Nutrients Organic Range.