Learning how to winterize a inground pool with sand filter is a job you want to get right the first time so you aren't dealing with cracked pipes or green slime in May. It's that time of year when the air gets crisp, the leaves start dropping, and the thought of jumping into the water makes you shiver instead of feel refreshed. Closing the pool isn't exactly a fun weekend project, but if you take it step-by-step, it's totally manageable.
The whole goal here is to protect your investment. Between the freezing temperatures and the debris that's bound to blow in, your pool equipment takes a beating over the winter. If you've got a sand filter, you've got a few specific tasks to handle to make sure that heavy tank doesn't turn into a giant block of ice and crack down the middle.
Get the water chemistry right first
Before you even touch the filter or the pump, you've got to make sure the water is balanced. This might seem weird since you're about to close it up, but it's actually the most important part of the process. If your pH is way off or your alkalinity is wonky, that water is going to sit against your liner or plaster for six months and cause all sorts of staining or scaling.
About a week before you plan to close, test the water. You're looking for a pH between 7.2 and 7.6 and alkalinity between 80 and 120 ppm. Once that's dialed in, go ahead and add your winterizing chemicals. Most people use a "winter kit" that includes a strong algaecide and some phosphate remover. Don't just dump them in and pull the plug, though. Let the pump run for at least 24 hours so everything gets mixed thoroughly.
Give the pool a deep clean
I know it's tempting to just throw the cover on and say "out of sight, out of mind," but any dirt or leaves left in the pool will rot. That leads to stains that are a total nightmare to scrub off in the spring. Spend some time vacuuming the floor and brushing the walls.
If there's a lot of debris, you might even want to vacuum to "waste" so you aren't putting all that gunk through your sand filter right before you shut it down. Once the pool is sparkling clean, you're ready to move on to the mechanical stuff.
How to handle the sand filter specifically
This is the part where most people get a little nervous, but it's actually pretty straightforward. Since we're focusing on how to winterize a inground pool with sand filter, the filter itself needs some special attention.
Start by giving the filter one last, long backwash. This flushes out any trapped dirt and oils from the sand bed so it doesn't sit there and turn into a crusty mess over the winter. After backwashing, set the valve to "rinse" for a minute, then turn the pump off.
Now, look at the bottom of that big sand tank. You'll see a small drain plug. Unscrew that and let the water trickle out. Be patient—this can take a while because the water has to seep through all that sand. Just leave the plug off (maybe put it in the pump basket so you don't lose it) and let it drain completely.
The big trick with the sand filter is the multiport valve. You'll notice a setting that usually says "Winter" or "Winterize." If you don't see that, just move the handle so it's sitting halfway between any two settings. This lifts the internal diverter up and keeps the rubber gasket from getting squished and stuck during the cold months. It also allows any trapped water inside the valve head to expand without cracking the plastic.
Lower the water level and drain the equipment
Next, you'll need to lower the water level. How far you go depends on what kind of cover you use. If you have a mesh safety cover, you usually drop the water to about 12 inches below the skimmer. If you have a solid tarp cover, you might only go a few inches below the skimmer.
Once the water is down, it's time to drain the rest of the gear. Pull the drain plugs on your pump housing, your heater (if you have one), and your chlorinator. I usually like to blow a little bit of air through them just to be sure. It's a good idea to store all these small plastic plugs in one spot—the pump strainer basket is the classic "safe spot" so you aren't hunting for them in the spring.
Blowing out the plumbing lines
This is the part that makes most DIYers sweat, but you can do it. You need to get the water out of the pipes so they don't freeze and burst underground. If you have a powerful shop vac, you can usually blow the lines out from the equipment pad.
Hook the hose up to the discharge side of the vac and blow air through the skimmer and the return lines. You'll see the water start to bubble and then eventually spray out. Once the line is clear, you'll need to plug it. For the skimmer, a lot of people use a "Gizzmo," which is basically a long hollow tube that screws into the hole. It acts as a plug but also absorbs any pressure if water gets in there and freezes.
For the return jets, use those black rubber expansion plugs. Tighten them down until they're snug. If you're really worried about the lines, you can pour some non-toxic RV antifreeze down them before you plug them up. Do not use automotive antifreeze—it's toxic and will ruin your pool water.
Removing accessories and the final cover
Take out the ladders, the handrails, and any over-the-wall cleaners. If you have pool lights that aren't winter-rated, you might need to unscrew them and let them sink to the bottom or pull them up onto the deck, depending on your setup.
Finally, it's time for the cover. If you're using a safety cover, make sure the springs are tightened properly so it's taut across the pool. If you're using a traditional tarp-style cover, make sure you have enough water bags or weights to keep it from blowing away in a winter storm.
A few last thoughts on the process
It feels like a lot of work when you're in the middle of it, but knowing how to winterize a inground pool with sand filter properly saves you so much money in the long run. If you leave water in that filter tank and it freezes, you're looking at hundreds of dollars for a new tank, plus the literal tons of sand you'll have to haul in and out.
Once everything is buttoned up, take one last walk around. Check that the multiport valve is in the winter position, make sure the pump is disconnected from the power or the breaker is flipped off, and double-check that your drain plugs are all accounted for.
Now you can head inside, grab a coffee, and forget about the pool until the birds start chirping again. You've done the hard work, and your pool is going to be way easier to open when the sun finally comes back out. Just remember to keep an eye on the cover if you get a massive snowload—sometimes a little bit of clearing off helps prevent the hardware from snapping under the weight. Enjoy your winter break from the "pool boy" duties!