Hey @ kyser!
Without having further info it's kind of difficult to find the right answer. Lets try anyway:
1. How much do you water them? Sometimes having yellowish leaves means that they got to much water
2. Are you using light-mix kind of soil? If you are using one, be sure when you have to start adding nutrients. Some of them are ready to start adding nutirients while others may be ready around 3rd week of grown.
3. Whats is the RH? You need to be around 60-75%
4. Whats your PH? It should be 6.3+
Hope I helped you out!