API are great, I enjoy mine. Reminds me of chemistry in HS. I'd suggest getting a kit rather than buying everything you need individually. Save you $ in the long run.
And yes, you could buy LR
off of others in your area. Could be hit or miss, depends on if they were doing similar things that you want to do. Some people would keep hitchhiking crabs that would hurt corals if they didn't want coral...and so on. It might be cheaper in the long run. I have a local friend from HS that I am holding some of my Caribbean LR
for for her tank. But since I just had all of my inverts die off in 24 hours...need to make sure that my latest LR
addition didn't have copper in it...something else you need to be wary of. Just let me say this, avoid Petco or bulk stores.
And adding the LR
wouldn't give you your nitrates or nitrites, it would start the process with your ammonia and move from nitrite to nitrate. For whatever reason mine didn't start on its own so I gave it some shrimp. Went really fast from there.