It will be hard to beat FP with a DIY. A tad pricey, but @ 1ml/gal a little goes a long way.
It is a very good product and I believe it is worth the money.
In theory, you can make your own version of FP but I doubt if it would be cheaper -- or stable in a reservoir.
This is made by GH so it's gotta be stable.
Thanks guys, so far I'm happy with it. I'm on my first run using it and everything looks great. My hydro store keeps giving me samples of it and rapid start/root.