Thanks. You can also dip some of your nute solution and pour it around the stem. At that age it doesn't have a big root system and I doubt any of the roots have reached the water yet. That will help get some nutes directly to the small roots you have. How often to do this depends on what medium you started your plants in. If it's rockwool, only do that every 3-4 days. Rockwool holds a lot of water and can cause problems if keep continuously soaked. At this stage they need more N than anything else. Make sure your nutrients are supplying enough.
I am using Fafard potting soil and I don't ever have any run off from my water I don't really water them with that much water. I'm using General Organics at about half strength. Bio root, bio thrive, caMg+ and root booster. I don't have exact amounts used but I did go light I read not to use to much nutes on autosGlad I was able to help. On your soil plant, that looks like a bit of P deficiency starting. I'll need some more information to help. What kind of soil, what nutrients, what is the strength of the nutrients. At what pH are you feeding and what is the pH of your run off?
I've seen that soil at my local supplier. They make several different ones, which do you have? I know that their soils don't contain any lime. Did you add any?
If your soil pH is off you could be having nutrient lockout, where the pH is out of the range where the nurtients can be properly utilized by the plant. Without a soil pH probe, the way to check it is to measure the pH of your run off water. In soil, it's always good to give enough so that about 10% runs out the bottom of the pot. You'll need to do that next watering and test the pH. Until we know what that number is we can't address your issue properly.
Humic acid can be given throughout the grow. It's not a nutrient per say, but aids in water retention and helps to make nutrients more available to the plant.