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Hi! Thanks a lot for your comment man.
I have been thinking about the ph and in fact I am resting the water 24 hours before irrigating. As soon as I can I am going to buy a ph meter because I am almost sure it is the problem.
Do you say that mulching does that?
It's the first time I use it and it's because everyone uses it and it's what the growshop sells. I used to use tree bark but I couldn't get it.
I will investigate and try not to use it for the following transplants
Thanks again for your help!

Yeah PH is hard, don't buy a Amazon PH own they don't work worth a crap.

I know I can't use my tap water as it's around 8.5 so it is way to high I have to use spring water.

The mulch I would say just get more nitrogen into the soil, and maybe a thinner layer of mulch

lol don't worry, I don't buy on amazon...I'm from Argentina.
And Yeah PH is hard. Your tap water is really bad man!
I know that there are test strips that are sold in aquariums but I don't know how effective they are.
I understood about the mulch,
I'll try a thinner layer then. You have a good eye, as the mulch I put on them is quite thick.
Thanks man!