People often ask if the order of adding things to their reservoirs matters.
The short answer is yes.
Do things in the order I recommend, and you'll be just fine.
As you add things to your reservoir, your pH level will fluctuate.
As a result, it's best to adjust your pH last, using a digital meter.
If you're using a product that I don't mention, follow that product's instructions if it indicates when it should be added to your reservoir.
In other words, what's on the label supersedes what I say here:

1. Fill your reservoir with purified reverse osmosis (R.
   O.
   ) water.
   Using a UV filter any incoming water into your reservoir ensures it's disease/pathogen free.
   
2. Add CalMag.
   
3. Add your additives, one at a time.
   You should have an air pump in addition to airstones so the water is circulating.
   Allow each of your additives to get mixed well before adding the next one.
   
4. Test PPMs using a digital TDS meter to make sure you aren't adding too much.
   You should only be at a third of your final desired PPMs.
   For instance, if your desired PPMs for a given week are to be at 1000 PPMs then you will not want to have more than 333 PPMs with your additives added to your water at this point.
   
5. Add your base nutrients until desired PPMs are achieved.
   Add nutrients slowly and use your TDS meter to make sure you don't go past your desired final number of PPMs.
   
6. Adjust your pH to between 5.
   8-6.
   2.
   

You aren't done yet! It's important to continue monitoring your reservoir's nutrient solution.
You're going to notice the water level goes down.
This is a result of evaporation combined with the plants drinking.
All you want to do is add more R.
O.
water.
Don't keep adding nutrient solution.
You lose water at a much faster rate than nutrients are used.
Remember to always adjust your pH level, even though you only added water, your pH can fluctuate.
Although you could use a formula to figure out how often to change your nutrient solution, I recommend keeping it simple; Change it once a week.
You will be rewarded with fewer problems related to diseases/pathogens.
Another advantage of changing your water once a week is that it's easier to clean your reservoir.
Simply use hot water and Bio Green Clean, available at your hydroponics store.
You can also use concentrated bleach to clean your pumps, airstones, etc.
The bottom line is that the cleaner you keep your grow room, and especially your reservoir, the better your plants will grow and bloom.