ILGM the company that sponsors this forum is a good source for seeds. They are very trustworthy. I’ve ordered multiple times without issues. They will replace seeds that don’t germinate.
Grand Daddy Purple is a high THC indica dominant strain. I just finished a grow of 3 of them. As a matter of fact the journal that you had ask your original question was for GDP and Green Crack.
I’m a soil guy, I’ve considered hydro but currently I’m limited by space and time. There’s many hydro growers on forum. I’m going to link a couple of journals of for hydro growers. These guys could probably help you out with questions about hydro growing. Just a heads up you can also use search feature to find just about any subject on forum just type in keywords. I also wanted to encourage you to read as many journals as possible and don’t be shy, invite people to follow your journal.