I'd suggest no using FP with early veg/seedlings. I think grow is a better choice at that stage. Start low and don't trust their feed charts either. Or at least be more careful with FP. I bought some FP 6 months ago and I've only used DG. Long story short when I bought it I had mothers and cuttings. I had no bad results with those plants. Since then I got spider mites. Eventually I culled most of library. I wanted to toss some strains others I wanted to search for a better pheno.
The first batch of seedlings were going great. I've never had a problem with seedlings or plants in veg ever. I started a second strain a month after the first. So when I noticed the old leaves of the first batch were starting to yellow and get brown spots. My first reaction was I was low on N because this issue I've had several times in early flower. Which is why I bought FP in the first place. Since it takes less FP to add N during flower I can use more bloom than if I were to use grow. Only this time it wasn't giving me the desired result. At this point the problem was starting to show up on my second batch. So I switched back to grow. I caught it in time on the second batch. Unfortunately the first batch I culled the females with the males and only kept the cuts of each female. I didn't want to start a flowering cycle with leaves yellowing and falling off. So for the time being I'm only using FP on well established plants. At this point I think young plants benefit from the added phosphorus and FP just can't provide that.