I assume you want to flower them then. As the others said HPS is better suited to the flower cycle.

Yes you can just change them from veg (MH) to flower (HPS) just that easy. (as long as the ballast are the proper ones or you have a switching ballast or conversion bulb)
Zandor Reviewed by Zandor on . Can you switch from MH to HPS Can you do this without affecting it im very sure you can there 1 month and 1 week old and i just switched from MH to HPS let me know you all please. Rating: 5