Leaves turning yellow and plants growing slowly. R...

Hi @Lukewarm! This looks like a nutrient deficiency, at this stage this is certainly Nitrogen. Are you sure you're growing in soil? Your medium looks more like coco to me, and coco does not contain any nutrient, so you need to add them into your waterings from the very beginning of your grow (start with a very slight EC then slowly increase nutrient intakes if the plants look healthy). Otherwise, seedlings in coco won't succeed without nutrients. This might also be related to under-watering but I guess you're checking the subtrate's dryness everyday? Roots need to be on a wet/dry cycle to properly spread, searching for water & nutrients, so your medium should alternate between wet -> slightly wet -> slightly dry -> wet (...) but never let the medium dry for too long especially if you're in coco. Now since you already applied some BioGrow this week, I think you solved the issue by yourself, but keep a close eye on them and see how it goes by the end of the week. Hope this will help, give us some good news soon, happy growing 👊