Plants absorb different nutrients much better at certain pH levels.What is pH anyway? When the purity of water is altered it can become "acidic" or more "basic". Water that is considered neutral has a pH of 7 on the pH scale of 0-14. If the water is "acidic" (on the low end of the scale) the water has more hydrogen ions than hydroxyl ions.If the water is "basic" (on the high end of the scale) the water contains more hydroxyl ions than hydrogen ions.
As you can see on the chart most nutrients are absorbed between 5.5-6.5. So we want to make sure our pH levels are within these parameters. If growing in soil pH should be a little higher.
So lets do this!!!
get a sample of nutrient solution. Half full at least.
Now place 3-5 drops of pH test solution in sample. If it turns "reddish" in color it is too "acidic",and if it turns more "blueish" in color than it is too "basic". In this case our sample is on the low end being too "reddish"! So we will add some pH up to our nutrient solution 1-2 mg per gallon at first.Then more if needed.
After rechecking our solution again it appears to be more of a "yellowish" color which means it is around 6.0 on the pH scale!
This is where we want to be. Remember when you add more water to your solution in the near future make sure the pH is adjusted before using. Keep in mind any nutrients or additives may change your solutions pH . Of course if our pH was too high we would have used pH down too lower it .link