Brown tips and discoloring of the leafs

Hello, last time I got fantastic help with my seedlings but now I have different problems und different plants agin and don't know if it's bad or normal.
I am a first time grower and my plants are in coco coir with 30 percent perlite. I use biobizz grow, activera and calmag and use it with tap water with a starting ec of 0.3. I feed my plants phed water with a of around 6 and an ec of 0.5 - 0.8. Now over night one plant got brown leaf Tipps, the other has the tips of the serated edge rolled upwards, am the third one has some weird discoloring. What do I do wrong and what do my plants have?

Bit more info, I use a 80cm x 80cm grow tent with a 180 Watt led panel on 80 percent around 30 - 40cm above the plants. Rh is around 50-65% and tells between 20c to 24c.

Would be nice if someone can help me

one possibility is that your light may be too close and the tiny root system cant keep up with the nutrient intake i sometimes have it with even bigger plants see if raising your lights to 50cm+ works

Ty, will try this out

Bump.
The one plant looks worse than yesterday. Is it a cal or mag deficiency? Or something else, someone an idea?