Dried Curled Leaves, slight brown spots, help!

[Agouti]

Lol that didn't work, here are the two plants.

 

[al70]

They look fine agouti, don't be panicking ✌

 

[Agouti]

Yeah the mg deficiency was really pronounced, but after letting the soil dry out, it's almost entirely gone.

 

[BigBozat]

Lol that didn't work, here are the two plants.

The first pic looks like leaf droop from overwatering.

The second pic doesn't look all that bad... between the slight fuzziness of the pic and all the factors previously mentioned in this thread, could be anything.

It could be early Mag def, as you're thinking, perhaps from all the leaching going on from excessive daily watering? (alkaline salts tend to leach out more easily than acidic ones).

Or not...

Mag def symptoms may begin to appear only on the portions of a leaf or the plant that are exposed to the sun, with the shaded portions of leaves remaining green.

Did you mention what the pH is?
Low pH can cause Mag def, too (as can drought conditions, poor drainage, or cold temps... also, calcium and potassium compete with magnesium for uptake by plant roots, and magnesium often loses).

If prior suggestions don't get results (try only one 'remedy' at a time, else no way to easily figure out which particular tweak worked), then maybe consider a foliar application of Epsom salt?

Uptake (of Mag) via foliar (spray of Epsom salt solution) should be [relatively] quite quick, so you should be able to tell fairly quickly whether it was indeed Mag def or not... if the foliar doesn't arrest/reverse the Mag def symptoms within, say, 24 ~ 48 hours, you can move prolly move on from worrying about Mag def...

Pro-Mix HP is basically just peat + perlite (roughly, 3:1), plus a bit o' wetting agent/surfactant and a dab o' mycos (and perhaps not even the best one for cannabis). Lacks nutrients, lacks mineralization... not what I would consider a well-rounded 'soil'... needs more humus/organic matter in the form of composts, EWC, etc. (which, in turn, would require additional aeration/drainage to be amended in as well, as the amount of perlite in the Pro-Mix may not be sufficient to balance the increased water-holding that additional humus/organic matter brings).

 

[BigBozat]

Yeah the mg deficiency was really pronounced, but after letting the soil dry out, it's almost entirely gone.

Oops, you must've posted this b4 I could finish posting my earlier note... so, never mind (lmao)!
If it WAS Mag def, likely your excessive/overly frequent watering leached it out.

 

[WifiSeedsPlz]

You may have started giving them nutes too soon. A lot of peeps wait until the 5th to 7th node to start giving them nutes. Also, was your Ph okay?