Blueberry

hey there future is green, your humidity is much too low, that's why , try using a mister or spraying the seedlings up to six times to maintain around 65% humidity. these might very well be stunted though, just bear that in mind in case you might want to consider a redo. Hope this helps ! 🚀

Has your ph reader been calibrated lately? Make sure your calibrated and lower your ph down to 5.7 to 5.8. Ec should be around the 800 ppm range right now. Keep your water cool, 62 to 68° is about the best. Add a little cal/mag once or twice a week as well. Watch for new growth to improve. Cheers

Most nutrient mixes will stain your roots a little bit. Unless they look mushy/slimey or stink, then you don't really have to worry. I always use hydroguard just in case though. I assume katana will have a similar effect of not letting bad bacteria establish a foothold.