WATERING QUESTION: Why are the pots still heavy? I use Plagron lightmix, 600w LED

You are new to growing, these are all valid questions. firstly let us break down the water molecule, we use RH (Humidity) to measure water content, everything in existence has a moisture content or RH% whether it be very dry (stone) or very moist (mud). Your soil or medium once drenched with water only normally has two options to get rid of that moisture within the soil, it can uptake through the root zone of the plant or it evaporates into the air given its warmth. Temperature greatly affects the rate of evaporation and you want it cool around the rootz with little fluctuations if possible. If you feed 300ml of water and uptakes only 200ml. When you water again the medium will be holding 400ml, moisture is your enemy if its allowed "Time" to stagnate Bacteria like fire need 3 things in order to grow, moisture, warmth, and time. Do not be afraid to let the plant leaves droop from drought, although it seems drastic the plants have defensive mechanisms that purposely droop leaves in defence long before any permanent dmg is done. Something else to look into and read up on is the pressure of your grow space, whether it blows up the tent (Positive pressure) or sucks in the tent (Negative pressure). work out the cubic feet of your space so the length, width, height, have an extraction fan on a cycle timer extracting out the tent, every exhaust fan has a CFM rating, cubic feet/minute, have the exhaust empty the tent periodically (every 10-30 min) for 1 minute or as much as needed. having a negative pressure consistently will draw all moisture out the soil/mediums once maintaining perfect cycles of drought/flood watering you will never have to worry about bugs/rot. Good luck.

What to do. Start a diary. Beyond that, they're only 3 weeks old and don't have a lot of root structure yet so of course they're not going to be drinking a lot. Don't overwater (overwatering is the state of being constantly wet)... don't give them anything more until the pot is light... and have patience... if you haven't drowned them, they'll be ok. Good luck.

if they dont consume - most prob ph is wrong, still if they are big enough for that pot, wait till they will drink BEFORE loading good ph watering into them/her while you have small plant in big pot - thats the game of small overwatering constantly in both ways - spraying twice daily with good ph water would help too ...

The problem is all the soil around the plant and top 3-4 inch are totaly dry but the pots still feel heavy on touch. Should I let them be without watering for more than 8,9 days? This seems funny because i watered only 200ml 7 days ago.