Can someone help me please? :(

Ph is too high in soil. Cannabis likes slightly acidic. You are experiencing a lock out. The ph controls what nutrition is absorbed best when. There is a balance between the right amounts of nutrition and the plants usage. When you figure out the levels then it's just adjusting it through course of grow. This will maintain a right ph via nutrition in soil or substrate.

The best way to use calmag is to add it to water till it gets to 0.2/0.4 EC or 252ppm max, then you add the fertilizers you need to add to feed them, this way is almost impossible to get to calcium toxicity so imho for the next grow you should get a EC or PPM meter.

calcium nitrate is a strong base, try adjusting your PH down toward 6. if you are combining calcium nitrate with a sulfate of potassium, then yes calcium sulfate will precipitate out in an insoluble form of calcium.

Thanks for the answers, it's my 1st grow and luckily only 1 in 4 plants has this issues. My grow is all organic, only with biobizz products so I think the problem is not the pH because I watering with ph 7 and the substrate buffer pH, so I think the problem is like you all said, toxity/overdose calmag because I watering all times with calmag. Next grow will be better, thanks a lot guys

And yes... you've overloaded on the calmag... just as @Organoman says... calmag should only be given once a week IF NEEDED....

Your problem is your PH... 7 is WAY too high for your plants to absorb the nutes they need.... which is why everything is looking pretty sad. Magnesium, for example, can only be absorbed by your plant when the PH is about 6.0 ... Do a flush with water PH'd to 6.0-6.3 and then keep the PH of everything you give her between 6.0 and 6.2 and she'll start taking on all the nutes she desperately needs... damaged leaves will NOT recover. Good luck...

I agree with Organoman. Once I applied calmag three times a week and all the plants ended up looking like yours. The plant seemed mostly OK but most of the leaves turned light green or yellow. My pH was correct but I attribute it to my over applying calmag.

This is a nutrients lockout you need to flush, this happens because of many things, ph, too much nutrients, not enough nutrients etc

Serious?? So it is the problem because i used calmag on all waterings when they started flowering :( luckily this issues only appeared in 1 plant (the last one). So next time I'll use calmag only 1x per week. Thanks for the help bro