Like I jokingly posted above, this hobby seems to constantly walk the tight rope of "don't over react, but don't get complacent and under react either!"
As a newbie with no experience at all, it feels impossible to know when it's time to fix something and when it's time to let it ride.
Always remember, its a hobby. Its supposed to be fun! If you spend the entire time worrying if you're doing something right or wrong you'll never be able to truly enjoy the hobby. In all honesty, I tend to lean to the side of always under react. If you're testing like you should be, its much more difficult to under react to the point of causing harm. For example, when my alk tests lower from the last time I tested I look at the trend line. If it was trending up, and suddenly it went down a little, I tend to not do anything. I wait until my next test and see where it is. Maybe my water change corrected it, maybe it was an inaccurate test, maybe it was an increase of growth due to the weather being nice and I had my windows open causing my PH to be a bit higher than normal any my corals liked that enough to grow a little faster. My next test will allow me to see the trend of the parameter. From there I can decide to either do nothing until the next time I test, or make a correction, but generally as long as I'm within my tolerance of my parameter goal, I'm happy.
If you're not sure when its time to step in and fix something or change something, try writing out a set of goals. IE: Alk: goal is 8 DKH but lets say plus or minus .5DKH realistically. Phosphates: Goal 0.08ppm but plus of minus 0.05ppm, Ect.
This will really help to guide you to make changes. If you need help with picking said numbers, I'm always happy to help. In reality the actual number is less important than maintaining a tolerance of fluctuation.
Personally I like to write out everything. Parameter goals, maintenance items with frequency, and overall goals. Even down to what and how I intend to dose, top off water, ect. Plus whenever I make a major change, for example switching from 2-part dosing to kalkwasser, it helps me to see what else that change might affect. For that instance I would also have to change the type of magnesium I'm dosing. Also, its perfectly normal if your goals change over time as you learn more. That's part of it!
A few other words of advise.
-Everyone runs their tank differently. Your own eyes will be able to tell you if you're on the right track or not. Don't fret if the way you do things or keep parameters is different from an experienced reefer.
-if a problem occurs, whether it was cause in a short time or over a long time, the best course of correction will likely take a long time. Small corrections, test, repeat. Corals will react even slower, so just give it time, things will turn around.
-I watch phosphates and ignore nitrates personally as they are somewhat corelated. I've found nitrates will be what they will be. That being said, I still test once a month or so to make sure nothing is getting out of hand.
-Magnesium. Its super important, IMO much more than nitrates. I test once a month. It doesn't get consumed at such a pace to require weekly testing. But just don't ignore it. Once again, if its low, I typically will correct the levels by two or three doses over the course of the next week or two, testing in between to watch how the dosages react within the tank.
-A little algae isn't a problem. All healthy tanks have a little somewhere. It doesn't make sense to turn the tank on its head to try to correct something that isn't a problem except in your eyes.
Good to know they're a good "canary" coral. 
