Are youy kidding me? They make a meter to to measure PPM's, damn whats next, a meter to measure PH? If only I had 3 or 4 of each. LOL

I dont get whats so confusing about the question so lets try a word problem, everyone likes word problems.

On Monday 10/31 Sally, wearing a pink halter top and bib overalls, filled the res with 72 gallons of water and added nutrients to the combined NPK of 10-17-34 and the PPM is 1109. 

Today on 11/11 and Billy Bob, wearing biboveralls, a tee shirt from Laconia Bike Week in 2012 and the pink halter under that, checks and the PPM is 1403 and the res has dropped 14 gallons. What is the NPK % of the water remaining in the res after he adds the 14 gallons? It wont be back at 1109 because because some nutrients have been consumed and there and probably root particles and bacteria shit. 

This is what I want to know, to find the NPK I need a meter becasue N + P + K=1403 is not enough information to find the variables. 

Now if you dont have the answer then just wish me a Happy Birthday. Turned 61 today,

Happy Belated Birthday.

I doubt it is worth the expense to you but you might take it to a lab or look into an ultraviolet spectrophotometer.

thanks