First grow ever, SensiSeeds Silver Haze Fem., Biobizz

Hello everyone. I'm Leon, happy to share with everyone my first ever grow. Firstly I use a whole set of Biobizz products. They seem to be beginnerfriendly, even if they are probably way to expensive. It got suggested by a friend, who also is a beginner. Right now in Germany they are many new companies trying to get big because of the legalization. Probably many are overprized. I started the germination of 3 seeds in a paper towel, which I soaked in water. I put it in a ziplock, wrapped it in dark cloth and put it on my heater, which had consistent 25° C. After 30h time I checked on them and boom! Every 3 of them already opened. I think I could have waited a bit longer, because they just popped and only had like 1-2mm of root length. Then I put them into my soil (BioBizz light mix 6,2ph), which I prewatered completly (I got rid of the excess water). I made the water have a ph of 6,6 with ph- and just let them sit there with 18h of light and 6h of darkness. I am constantly watching growers on YouTube (really hard in what to believe or not, every person and strain has it's own methods) to learn and get some knowledge. Thats also the reason why I'm sharing this with you. Honestly, I've never had plant in my life, but I always hated to get my stash in a random place. So after legalization in Germany it was time to connect to this subject even more. So as you can see everyone of them grew fine, but I think they might be a little slow (might be the high ph-Level of the first watering, 6,0ph is recommended I guess). I think they try to build the roots right now, so I don't stress about it and let them do their thing. Because I am new and really nervous I opened the tent pretty often, maybe 3 or 5 times a day, which probably disrupts them. The reason why is because I haven't really finished my setup in the beginning and I changed some settings because of the many different information I got. Till now you can say I constantly held like 25° C and 65%-70% RH at daytime and 21° C and same humidity at night. My lights a 30 cm above my seedlings with 30%/100% dimming. I have a clip fan for circulation (blowing on tent wall, not the plants) and the inlinefan is activated on 20% strength. But I firstly activated them on day 3. After week 1 I start running the clip fan lightly into the plant direction for thickness. Maybe I am going to add some Cal-Mag on week 3 for 2 plants. If anyone is seeing this: What do I have to pay attention to for sativas? I heard they get really big and stretch twice or thrice the size when starting flowering (tent height 160 cm). When should I start using my fertilizers? I am using tab-water (7,5 ph, i have no EC or TDS measurement, no water analysis done). My plan: Just watering all 3 babys till week 2 or 3 till I change the pot to 13L (final size). Wait 1 week for them to develop roots and then use the first dose of Biobizz Grow. But I have the idea to try on 2 plants a low dosage of Cal-Mag before puttings them a new pot. Generally said: I don't want to burn them. I am looking forward to top them and additionally use some LST to get them wide instead of high because my tent is only 160 cm. These sativas might get really big. Now I dont even know in what week I start flowering. They probably grow for 6 weeks before it is worthy to flower. I will just make it depend of the plant size.