It looks to me like a little mag def. The reason i say this is cause the leaves are dark in the middle and get lighter towards the edge. This will happen if your phd water is 6.4 and lower. I use FFOF also and havent had any problems during veg so thats why im questioning the ph. If i remember right molasses will drop the ph? Try watering with 6.8 the next couple waterings and see if that helps. Im just guessing here so even if i am wrong raising the ph a little wont kill anything haha

Also, was the hydroton soaked in phd water before you put it on top of the pots?