It can be extremely overwhelming, there is a lot of information, a lot of conflicting information and more than one way to achieve the same goal.
For chemistry I always go to Randy Holmes- Farley our resident chemistry expert.
https://www.reef2reef.com/forums/reef-chemistry-by-randy-holmes-farley.295/
Your chemistry questions will be addressed regardless of you skill level, be proactive and create threads. In layman terms alkalinity is a solutions ability to maintain it's pH value. Charcoal is a medium used to remove pollutants and to a lesser extent some dissolved organics, some use it to polish the water (remove yellow tint) or to absorb potential toxins created by corals.
Nitrates are the end result of the nitrogen cycle.
1. Metabolism by livestock produces ammonia which is toxic to fish and inverts. Ammonia is also produced by organic decay, such as uneaten foods, death of livestock or bacteria.
2. There are types of bacteria that utilize that ammonia and convert the ammonia to nitrites, nitrites are still toxic, another group of bacteria utilize the nitrites and produce nitrates which is not toxic as the appropriate levels.
Rastas as with many zoanthids can be tricky.
The easiest and best intervention for your corals and fish are routine water changes to remove pollutants and replenish elements.
Please create threads with your concerns, everyone has been in the same boat and others have the same questions.