Next time plant seedling sprouted in rockwool in a half empty cup. So when they stretch you can cover remaining of stem in cup with perlite. All that stem will be covered and become sexy white roots.
Little trick as well. Use cheap white vinegar for ph down when adjusting ph with plain water or nutes. It will save you a lot of money in the long run.
NEVER GIVE UP. She will bounce back, they are a very hardy plant man and they deserve more credit. you will diminish your yield and also delay your harvest with these probs but. You will learn from your mistakes.
Was the soil pre -ferted to start with? Slow release fert? what is the ph of soil? what ph water are you feeding? how often are you feeding nutes and at what ph and at what dose? You have nute lock out. Fush with plain phd water and let dry out. Go hempy bucket and you wont have any of these...