By Alicia Stephens and Anjelica Swanson
People purchase hot tubs for many different reasons, including health benefits, therapeutic massage, and overall relaxation.
Regardless of the motivation to purchase, hot tub users want their ownership experience to be as easy and trouble-free as possible. However, due to the hot water and aeration that are key elements to hot tubs, their maintenance can be challenging. Therefore, establishing an effective maintenance routine that includes testing the water regularly is key to keeping them clean, clear, and ready for use. Many hot tub owners are unaware of the challenges phosphates can cause. Consistently testing for and removing phosphates is important to ensuring an effective hot tub water maintenance program.
What is a phosphate?
There are many different types of phosphates and phosphoric acids; however, the form tested in pools and hot tubs is orthophosphate. These nuisance phosphate-based compounds are formed when a phosphorous-containing compound, such as polyphosphate or a phosphonate, react with oxygen in an oxidation-reduction reaction. The usual cause of this reaction is from the addition of chlorine into a pool when a phosphorous-containing substance is already present in pool water. Not all phosphorous-based compounds are problematic. In fact, there are many different phosphorous-based products used in water treatment applications due to their efficacy and ease of use. It is the end product, orthophosphate, which provides no benefit to hot tub water but, instead, reacts with normally soluble minerals to form insoluble compounds that may lead to poor water quality or create other problems in hot tubs.
Where do phosphates come from?
The goal for hot tub maintenance is to sustain a phosphate level of less than 125 parts per billion (ppb) in the water. Maintaining this level can be a challenge due to the almost constant introduction of phosphate-containing contaminants into the hot tub environment. Phosphates enter hot tubs from many different sources. Outdoors, for example, fertilizers and other lawn-treatment products may contain phosphates that can inadvertently be carried into the water by wind or rain runoff from the yard. Phosphates can also be unintentionally added into hot tubs from the soaps, cosmetics, and detergents used by bathers, as well as through their urine and sweat. Environmental factors such as dust, plant debris, some source water (including wells), and soil are additional sources of phosphates.
Certain specialty products, such as sequestering or chelating agents, contain phosphonic or phosphoric acid, which eventually break down into orthophosphate in the water. Stain and scale-control products often contain phosphorous-based compounds due to their best-in-class control of scale, which is prevalent in the warm water environment in hot tubs. These products also help prevent iron and copper staining or water discolouration due to metals, and some will help prevent corrosion. Many municipalities add phosphorous-based scale products at water-treatment plants to help reduce buildup and prevent corrosion in the distribution lines. In fact, it is not uncommon for some areas to have readings between 500 and 1000 ppb straight from the tap.
