My plant is drooping and some has curling yellow leaves on them. What could possible cause this?

These articles below will help you identify the symptoms and inform you on how to fix the nutrient lockout or deficiencies in your plants.

Plant Stress: Why Your Grow Lights, Nutrients, and Buckets Might be Harming Your Plants
The Best Way to Fix Nutrient Lockout and How to Prevent It
Heavy Metal Deficiencies: Identifying & Treating Boron, Iron, Magnesium, and Manganese Issues
Grower Q&A: Why Are My Leaves Turning Yellow?
Identifying and Treating Nitrogen Deficiencies In Your Plant