problem with the soil Biobizz light mix

A VPD that is too high means drier air and increased evaporation and transpiration. Too low a VPD can lead to slowed transpiration and reduced growth. It is VPD that drives transpiration and nutrient uptake in plants; the uptake of water at the roots is determined by the loss of water through the shoots, and the loss of water through the shoots is determined by how much water is in the air. Perlite will help but won't solveyour problem. Highly recommended you read up Bruce bugbees videos on yourirbe with regard to the 9 cardinal rules of plant growth, how they all rely on each part of the process to run in unison. Water won't move because it has no where to go. Evaporation, drainage or uptake. Moisture not wicking from one atmosphere to another. Good luck.

So, if you have a young plant. If you had 200ml in a 2l pot. It stays wet for 10+ days. Generally it's just cause the pheno is needing s lot less..when she grows up. She's drink more

That's coco coir, so 2 parts coco : 1 part drainage amendment, or ~33% Being exact isn't necessary. Include any existing perlite in the calculation. e.g. pro-mix hp comes with 20-25% in it already, so it takes a little algebra to find the unknown X% of perlite to add.

Ussually its around 30%. I was puting 5-7 liters into 30-40 liters pots and if its big enough plant it never lasted longer than 2-5 days for me.

I think your using a pot that's to big for the size of the plant, Might just need to wait till it grows into it. Or next run utilize transplanting them. BioBizz light mix is a combination of Peat moss Sphagnum peat Perlite Black peat White peat Compost Worm cast Its more of a soilless IMO then it is a true soil. The compost and worm castings help but their is so little of them vs all the different grades of peat. With peat moss heavy substrates min 30% perlite is ideal. But I have not seen many add extra into biobizz and use it as is.

I use light mix, not sure what % perlite is but it's enough. If your in 20L pot and the plants small then it will take a while to dry out. I'm in 12L pots and it takes about 3-4 days before next watering and my plants are week 4 at the moment. Check out my newer diaries as I have done very detailed notes on watering in light mix.