Hopefully things are going better for you... assuming you're using good quality nutrients I wouldn't understand why you're seeing this so early on. Typically when I see problems like this, I simply flush the plant with a low strength mix of base nutrients only. By low strength I mean NO MORE than 1 ml per liter of water of A and B. If you're meausring the PPM of the mix, you should be somewhere around 350-450 ppm with the solution you use. Put enough in the plant to get run through and remove the excess from the drip pan on your planters. Curious, why do you have expanded clay pellets in the pots?

One other suggestion.. kick your Ph up to a range around 6.1 - 6.3. Being to acidic can also cause uptake problems.

Peace,

Farmer Rich