How I Increase Hydroponic Nutrient Concentrations (WITHOUT an EC/TDS Meter)

Eventually I will get an EC meter, but for now, I just give the plants the minimum and slowly build upward.

Nutrient concentrations have always been the toughest part of hydroponics for me. While I don't have it 100% figured out, I will write about how I do things. 

What I have been using for lettuce is General Hydroponics MaxiGro. On the package, it says to feed the plants a concentration of 5-10 grams per 4 liters. For my yogurt container system, the fill level to the bottom of each net pot is 600 milliliters (or 0.6 liters). So each of my "reservoirs" is 0.6 liters. So to start them out with the minimum level of 5 grams per 4 liters, I need to know how many grams go into 0.6 L to achieve that same concentration.

You want to setup an proportion with an unknown (how many grams per 0.6 L). Here is a good tutorial on proportions if you need a refresher. Here is what I did:

So I started my plants off at the minimum, because as you probably know, you don't want to overload your plants with too much nutrient. But the question remains: how soon should you increase the concentration?

It's a shame the plants can't talk and just tell you when they're wanting more food. What I've done is just experiment with when to increase the nutrient. I started a batch of lettuce with the minimum and then tried upping the concentration from the minumum (5g/4L) to 7g/4L. It works for the yogurt containers system because it is very convenient and quick to change out a 600 mL reservoir. Recently I went from the minimum concentration to a 7g/4L concentration 5 days after being in the minimum concentration (ten days after of the seeds emerged).

Maybe soon I will get an EC/PPM meter and will be able to more accurately gauge when the plants need more nutrients. Until then, this method seems to be working out just fine.