What causes sand to enter the pool and gather under the jet(s)?
The most likely cause is a defective “underdrain” or “lateral” in the bottom of your sand filter. If an “underdrain” or “lateral” is broken, sand will escape the filter and be carried into the pool by the flow of water and usually collects under the jets. It will be necessary to dismantle the filter, remove any remaining filter sand and replace the defective parts.
