Lowryders

@AsNoriu, got it, thank you so much!! I actually didn't give them any BioGrow until I repotted them, but when I first planted them in their nursery pots I reused some of the soil from my previous grow; like the parts of it that weren't penetrated by any roots. Now I see it where the build up is coming from: the soil I used was likely packed with all the nutrients that the previous plant couldn't absorb. I'm gonna stick to your advice, and given that now they got access to lots of fresh soil, I hope they recover soon! Thanks again for your input :)