A while back I e-mailed GH the question "Do tomato's need extra calcium" this was there reply;
"Calcium effects the plant's ability to uptake all sorts of
nutrients. This is why it is recommended to supplement with Calcium when growing plants that consume a lot of it (such as tomatoes). You most likely won't be able to pinpoint a Calcium deficiency on the plant, because it can appear as a plethora of other deficiencies. Nutrition in Hydroponics is a building block philosophy. Once you have low concentrations of one element, the rest react differently to other elements, and this can start a chain of lockout. Very few growers will know that this all started with Calcium. In your particular case, I would recommend using a CaMg product from the beginning of their lives to the end. That way you won't have to play the guessing game of nutrition manipulation and you will be providing them with the CaMg that they require."
This is the
CaMg that GH recommends, I forget exactly how much they recommend using but I would e-mail them at:
tech@genhydro.com to find out. I never did get any (I had no money) but someone gave me some calcium nitrate, and I've been using that. Though I still don't know exactly how much of it to use, I'm currently adding it at about 5mL (1 tsp) per gallon. Any calcium supplement that you use should made for hydroponics, or it wont be usable to hydroponic plants.