Don't use ferts yet.
Your pH is likely low, your soil looks soggy, and the symptoms are consistent with that.
If you use a pre-ferted soil, it's good practice to add EXTRA perlite. All those MG products are peat-based and the water retention qualities don't suit cannabis.
Those pots have drip trays built in, right? Remove them.
Go back to tap water. The pH 7 and the minerals in it will help offset the acids present n the peat.
Flush well with tap water and then allow to dry. If you can drill holes in the sides of the pots, that will help it dry out faster.
You can also do a foliar-feed with a VERY weak fert solution. Weaker than the bottle says.