Yes. The directions on your
nutrient bottle should say that if you added say one teaspoon of solution per gallon of water will give you a PPM of say 1000 PPM. So if you wanted to keep your solution at 1000 PPM Every time you need to add water to your tank you would put 1 teaspoon of concentrated nutrient solution to every gallon of water you add to your tank.
I just got a flyer in the mail from
Aquatic Eco-Systems, Inc. and they have waterproof TDS (PPM) Pens and pH Testers
for $55.50 You can't do much better than that.