How do you know if your filtration sand is clean enough?
It might seem a bit odd to wash sand, but it is one of the most important things you do when building a biosand filter. Don't forget to also wash your gravel! Selecting the best available sand, sieving it to get the right size grains, and washing your sand and gravel properly will minimize the turbidity and contamination of the filtered water.
Here are some resources to support you with this process: