Micronutrients

​Did you know?

Micronutrients can indirectly contribute to chlorine "demand". Microorganisms need nutrients to live, grow and reproduce. Certain micronutrients can impact pool chemistry in a few different ways.

One of those nutrients, nitrogen, comes in many forms, such as ammonia, ammonium, urea and nitrates. It serves as food for living contaminants in water. But it also combines with chlorine in some very complex chemical reactions with multiple stages, requiring more and more chlorine to eradicate it, in the process of breakpoint chlorination. The nitrogen compounds directly increase chlorine demand.

​Another micronutrient, phosphate, also contributes to chlorine demand. However, it does so indirectly. Phosphates fuel the growth rate of microorganisms such as algae. Then these reproducing contaminants use up the chlorine. It’s understandable 

that many believe chlorine reacts to and destroys phosphates directly, leading to increased chlorine demand — even we were taught that for years! But that’s not the case. In fact, chlorine and phosphate don’t even interact in the water.

Think about it: have you ever shocked a green pool that was overcome with algae? Where was the chlorine level the next day? If it was low or even gone, chances are your chlorine was reduced by 

​generation after generation of spawning algae. You had plenty of killing power with your chlorine (and perhaps an algaecide too), but because the generations kept coming back, the chlorine eventually got used up. You never removed the nutrients.
Unlike nitrogen compounds, phosphates can be easily removed, but this is done through the use of phosphate removers, not chlorine.
So if you’re facing a high chlorine demand, direct sunlight may not be the culprit. Perhaps it’s oxidation of bather waste or nitrogen compounds; or the repeated sanitization of rapidly reproducing microorganisms such as algae. We recommend supplementing chlorine accordingly, because we are relying on it to do many jobs."
Excerpt from Pool & Spa News
https://www.poolspanews.com/how-to/maintenance/the-finer-points-of-water-treatment_o