thanks tom, i will look into it, looks like Potassium ascorbate can be found easily but the problem is messurment, unless there is calc like WET's calc which can break down the numbers for us.
Monoammonium Phosphate also sounds good, it will provide P and NH4, but messurment might be a problem IMO. it is also good for acidic solution, which we are trying to make.
am not expert but here i go
Monopotassium phosphate 136.086 g/mol
Monoammonium Phosphate 115.03 g mol−1
so we will add about 10% more of Monoammonium Phosphate vs Monopotassium phosphate in the solution to get same amount of P??
i guess no one knows??