18/07/2026
A great guide from one of my suppliers. I've seen a spike in phosphate and wanted to share some info about what and how phosphate can get into your pool AND the impact it can have.
Based on the weather pattern across western Victoria over the last six months, including Bacchus Marsh, Ballarat, Melton and Sunbury, several factors line up with what you’re seeing.
1. Extended dry period followed by rainfall (the biggest factor)
Victoria experienced a relatively dry and warm summer, with below-average rainfall across much of the south, allowing dust, organic matter, bird droppings, fertiliser residues and pollen to accumulate on roofs, paving and gardens.
When rain finally arrived during late autumn and winter, all of that material was washed into pools in a concentrated “first flush”. This is one of the most common causes of widespread phosphate increases.
2. More runoff from saturated ground
Once soils become wet, subsequent rainfall creates much more surface runoff rather than soaking into the ground. That runoff carries:
* lawn fertilisers
* decomposing vegetation
* animal waste
* soil particles containing phosphorus
into stormwater and, ultimately, into swimming pools. Victorian water authorities note that wetter periods increase phosphorus transport through catchments.
3. Wind events
If you’ve noticed the issue from Ballarat through Melton and Sunbury, wind may also be contributing.
Strong winds transport:
* dust
* pollen
* dried grass
* agricultural soil
* organic debris
These materials all contain phosphorus. Pools with automatic covers often trap this fine dust, which then dissolves into the water when the cover is opened.
4. Increased organic load
You’ve probably also noticed:
* more gum leaves
* blossom
* seed pods
* decaying plant material
As this decomposes it releases phosphate into the water.