thanks much, I am glad you are enjoying the DIY threads, and I hope that they help save you some money so you have more to spend on seeds 
As far as phosphorous, fertilizer/soil pH controls much of the phosphorus availability to plants, so the best way to keep phosphorous available to your plant is to closely monitor the PH.
The Hammerhead and MOAB are both PK boosters you can make yourself for pennies.