Pev seeds and 2 other sativas

Hi to you! Today: solo photoshoot for girls! I thought that at this stage of development you might like to enjoy more detailed photos. And I did well. I noticed that Sideral (which is on the back of the box) was showing signs of nitrogen deficiency. So general tour of alga grow! With the installation of the small radiator at ground level, the water evaporates faster and the girls are thirsty more regularly. This week I have alternated the waterings: once green sensation alone, once CaMg alone, once alga grow. Obviously, they are quite successful (except Sideral who obviously has a high nitrogen demand from the start). Moreover, I wondered about the purple coloring of the leaf stems: Phenos like Sideral do not normally tend to color at the end of flowering (unlike Wedding Cake for example). However, the stems are already quite purple! The phenomenon worries me and is not improving. I know low temperatures cause stress causing staining, but that much ??? The worst part of all this is that the plants do not seem to suffer too much (I may be wrong ...). I don't know what to think anymore: UV's and IR's of led light? An excess of something (my soil partly comes from a previous harvest ... poorly rinsed?) In short, give me your opinion, advice on this. The plants are in a critical phase and I don't feel like pushing them around. For the rest, nothing very special, everything is going pretty well. Thank you for taking the time to read me ! See you.