@WildBill - Thanks for looking. Definitely could be hungry. I did a slurry test initially on the soil as I hadn't used it before and it was recommended for some fruit trees I was planting. Runs a bit hot in the 600-700ppm range. The shop said it had loads of nutrients in it and shouldn't need anything for a while. I was worried about burning up the seedling so I've been trying to run just low ppm distilled pH'ed water through it.
You think I should start maybe 1/4 strength or less, say 100ppm nutes? It's at about week 3.