A few pointers for ya:

I have grown using a Wafterfarm and you will have one hell of a good harvest with them!

I cannot tell from your picture, but if you don't have an airstone running in each WF, I suggest you get them. You can buy the air pump and airstone at any pet store, for about $6 total per WF. This allows the solution to become oxygenated, which helps promote plant growth and health. Have it run when the light is on or you can run them 24/7.

Secondly, I hope you have enough space to grow two plants. I use just one WF in a C13 cabinet which measures 24"x30" and that one plant fills the entire cabinet. Therefore, I hope you have an area at least half again the size of my cabinet. Otherwise, the plants will fight each other for light and may hurt your yield and possibly their health.

The GH nutes are quite good. I am using them for the first time and it sounds like you are enjoying them as well. Great!

Also, keep in mind that you won't want the plant any closer than 6" from the HPS' hood, if it is air-cooled and enclosed in glass. If your hood isn't air-cooled, you won't want the plants any closer than 12". Maybe more. This means you need to consider how tall you can allow your plants to grow. And, since your plants' height will double during flowering, you may want to start flowering now, if you haven't already. Besides, IIRC, a 400W lamp is no good at distances of more than 4 feet. If I am wrong, please someone correct me.

Since it's been at least a month since you took that picture, I am sure your plants are much taller now. So, you probably should start flowering now, if you haven't done so already.

Let us know how it comes along! I'd love to hear how much you harvest.