How long should nutrient last

[GpsFrontier]

I read somewhere that strawberry plants require a minimum of .5 liters per plant of nutrient solution. Assuming this is true, I have 32 strawberry plants and they would require 16 liters or about 4 gallons of nutrient solution. I think that was for one week and should be changed every week. I have a 50 gallon nutrient tank feeding these 32 strawberry plants and assuming that they require 4 gallons of nutrient's per week to feed on, then the 50 gallon's of nutrient should last 12.5 weeks before needing to be changed (provided that nothing is growing in it or contaminated it) and topping off the reservoir with fresh water so that is always at 50 gallons. My question is, is my thinking about how long the nutrients should last before being used up correct or am I not even close? I am using the Flora series nutrients and try to keep the ph at (6.0). I don't have a ppm meter though I want to get one in the future when the funds are available for it.