When Do I Backwash My Sand Filter?
Before we get to the answer, this article relates only to sand filters. NOT cartridge or Diatomaceous Earth (DE) filters.
Short answer: It depends on what your equipment manufacturer recommends. Check the manual that came with your filter or see if you can find it online. If you don’t have the manual or can’t find it online, you’re stuck with the long answer.
Long Answer: Backwashing your sand filter is extremely important when it comes to keeping your pool’s water clear. A filter that is bogged down with debris is not effective and causes a lot of strain on other components of your pool’s circulation system. It’s important to backwash only when needed. How do you know when to do that? Glad you asked. But first, we need to explain some stuff.
Your sand filter has a multi-port valve that directs the water where you want it to go. There are different positions for different uses. When the multi-port is in the “Filter” position, it sends water into the filter housing in an even pattern. The water hits the bed of sand and is filtered as it travels toward the bottom. At the bottom of the filter, buried in sand, are “Laterals”. Your filter’s size and manufacturer dictate’s the number and configuration of the laterals. Clean water goes through the laterals, up a pipe in the middle of the filter, and then back to the pool. It’s cooler than that, but for the sake of this, pretend it’s that.
The laterals in your sand filter get brittle over time. They sit in chlorinated water all year, have water moving through them under pressure, and are made of plastic. Too much backwashing can put undue stress on them and cause them to fail. If you see sand under your pool’s return jets, this could be the cause. And unfortunately, the only way to tell if a lateral is damaged is by taking out all the sand and inspecting them.
Too much backwashing also wastes water and sand. With each backwash, you are sending gallons and gallons of water to waste. In that water are the chemicals you paid for, and some sand from your filter. And of course, the water.
Too little backwashing can also cause issues with the sand in your filter. Continuous filtering of water without backwashing sends debris deeper and deeper into the sand bed. The sand can also begin to compact and water “tunnels” to the bottom, forming channels in the sand and bypassing the filter aspect altogether. This leads to poor water clarity and quality.
I know, you didn’t ask about any of this. I think it’s important to know these things though. Our goal is to educate pool owners. Swimming pools are an investment and we don’t want you out there willy-nilly throwing money into the ground. Breaking a lateral is an expensive repair. Come to think of it, most repairs are expensive.
The drawn out answer that will suffice for most filters is 8 to 10 psi above the starting pressure. These values can be found on the pressure gauge on the multi-port on your sand filter. If you’re filter is anything like mine, it probably needs replaced. If you hire a pool company to look after your pool, hopefully they replace them as needed. It’s an easy fix and they are cheap. Like cheaper than going through a drive thru for coffee.
Give your filter a good back wash, set the multi-port back to filter, turn on the system, and record the starting reading. There is no magic answer for what your starting reading is. All systems are different based on the underground piping, the size of the pump, the size of the filter, and any ancillary equipment you might have installed. Most gauges will have a plastic ring on the outside with two arrows. One will say “Start” and the other will be “Clean Filter” or something to that effect. Rotate the ring so that the “Start” arrow is pointing to your starting value. When the needle in the pressure gauge reaches the “Clean Filter” arrow on the outside ring, you will know when you need to backwash. But if you don’t have a gauge with the cool arrows, just write down the starting pressure, and when it reaches 8 - 10 psi above that, give it the ole backwash.
So, there you have it. No more guessing. No more wasted water and chemicals. Just good, clean fun (and filters).
Follow all applicable laws, regulations, and guidelines. This article is intended for informational purposes only and we are not held liable for any injuries or damages resulting from the information contained in it, or failure to follow applicable laws and/or manufacture recommendations. Please reach out to us if you need something clarified. This article in no way claims to be all encompassing of sand filters, nor diagnosing any problems. We follow and adhere to local regulations and the most updated version of the Model Aquatic Health Code.
