You may want to be very careful with the boric salts, if you may choose to use any of it, for it may be best to use a very -very- very small amount of it if you choose to do so!
You may be much safer to use the Epsom Salt to help bring the Nitrogen into ratio with the other minerals in the plant, so as to solve your problem!
Also , use of the kelp may enable the plants to take in more Nitrogen from the air, thus it may cause you more problems with the plants which may have this problem to begin with!