Magnesium deficiency in hydroponics?

Hi everyone. I found out that. The four of my aurora indica plants have magnesium deficiency. As this much is know how would i go about fixing this problem?

I read that epsom salt and other stuff could be used but how much would i mix into the bucket. The buckets are 2 gallons and i have two plants in each.

Actually guys, if its kool with everyone, i will answer my own question. I found in a book that 1 teaspoon (4.9cc) of epsom salt per gallon. Information was found in Ed Rosenthal's growers handbook.

u can also use un-sulphured molasses at the rate of 1tsp per gal of water, brings in the sugers for the microbes too