Hey @Andi_M8
first of all, welcome to our community, and let’s quickly get to your first post concerning CalMag problems.
CalMag deficiency can arise from irrigation water if there is too little Calcium / Magnesium in it. However, even if there is enough in the soil, other factors play a role in whether a deficiency occurs or not. Even a microclimate directly around the plants can trigger this deficiency. Here, it should be tested whether it helps to slightly increase the temperature and/or lower the humidity.
CalMag deficiency does not only appear in the third flowering week!
It usually already exists during the vegetative phase and manifests itself through tiny brown spots on the foliage, and especially then, one should do something about it, because - if it slips into flowering, there is usually nothing left to fix with this deficiency. Yield losses can then be the consequence.
It becomes very noticeable during the flowering period because generally now, i.e., in the first 4 flowering weeks / stretch phase, the plant needs a lot of nutrients.
Now you are working with Greenhouse Feeding.
I know it, but I haven’t worked with it myself yet.
In principle, it’s like Living Soil, Bio Tabs, meaning a purely organic matter where plants are nourished specifically by fungi and bacteria in the soil.
With that, there should actually already be enough Calcium Magnesium in the soil.
If the ambient air temperature drops too low during the dark period, this can restrict the activity of beneficial soil organisms, which can then lead to such problems.
Let’s make sure that the temperature doesn’t drop below 22 degrees during the dark period.
A minimal CalMag deficiency can be seen in your first picture.
But so slight that I wouldn’t worry about it.
In your post to @herr_gruen from 3 hours ago, your plants look " TOP ".
Many would be licking their fingers at that. 
It is possible to add some Dolomite lime to get even more Calcium/Magnesium into the soil.
Since you are working organically, I recommend the Dolomite lime from Bio2Grow!
Also purely organic, and at the beginning of the soil mix, simply mix in 0.5 to 1 gram per liter of soil. This means for a 20-liter pot, 10 to 20 grams, and no more. Lime can change the pH, so handle it gently.
It breaks down slowly over weeks and months, thus providing an extra portion of the desired substances.
With many liquid CalMag products, it can happen that soil life can be disturbed, weakened, or completely brought to a halt. Especially with mineral substances.
Especially with CalMag deficiency, it is better to work preventatively to avoid getting it in the first place. And as mentioned, if it’s already in flowering, there’s nothing more to be done.
And that’s how it is!
The quantities I mentioned to you are manufacturer specifications, which are always a bit higher anyway, and therefore it doesn’t hurt to always stay a bit lower than what is written.
To get the correct lime amount for the soil, a soil analysis would have to be done to determine the exact lime value.
I transferred the quantities to you from my Dolomite lime bag. It says so on the back.
In any case, your current grow will be a very good grow!
I think this helps you further, and I have to get back to my duties now. Have a nice evening, wishes Pflanzenpaule
. Current daytime temperature is 24-25. Night temperature at 20 (thought 18 would be better because at night). Luckily, the deficiency has always only appeared for me in flowering week 3. I also looked at the water values,
