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    The Complete Guide to Inground Pool Winterization

    September 11, 2014


    Around this time of year, we start to get those phone calls "Hey, Chris! Remember me? Well, we have a great first season with the pool, and now I'm wondering if I can pick your brain one more time..." To which I respond, "Closing the pool? Sure, you have a pen and paper ready?"

    When an inground pool is built by a pool builder, there is often a clause in the contract that calls for the pool builder to close the pool the first year, which may be included in the pool cost, or more likely, it's an additional expense, along with the cost for the winter pool cover, closing chemicals and other supplies like plugs and antifreeze.

    When you build your own inground pool, like I did in 2004, winterizing the pool is something that seems daunting the first time you do it, but after you do it once, and then open the pool in the spring to no problems, you wonder why local pool companies charge so much money to do it.

    Closing an inground swimming pool is something that any handy homeowner can do - in Ten Easy Steps.


    Step one should be done several days before you close the pool. It's important to check and balance ALL of the chemical levels, not just pH and chlorine. If you do not have a complete test kit, take a water sample to a local pool store to check your Total Alkalinity and Calcium Hardness levels. Alkalinity should be 80-120 ppm, and hardness should be 180-220 ppm. If they are not in range, add the chemicals needed to raise or lower them.

    It's super important to have balanced water before closing the pool - remember that your pool water won't be circulating or filtering for over 6 months, which makes it easier for stains and deposits to occur, or weaken a vinyl pool liner. If your pool water is hard (over 250ppm), or if you have high metals and minerals (well water), you should add a Stain & Scale chemical at this time, and allow it to circulate throughout the pool before lowering the water for winterization.

    After you check and adjust pH, alkalinity and hardness, circulate the water for several hours, or overnight. Then super-shock the pool to kill any bacteria and raise the chlorine level to a higher than normal level. This is generally 1 lb of shock per 10,000 gallons, but it wouldn't hurt to add a little more. Be sure to pre-dissolve the shock into a bucket of water, and then pour it around the pool, unless you are using a more expensive pool shock that is safe for vinyl liners.


    Closing the pool clean is very important - to prevent stains and chemical loss. Just like a favorite shirt, if you leave clothes dirty for long periods of time, stains will set-in and become nearly impossible to remove. Leaves, algae, dirt and dust that is left in the pool over the winter will make stains that will leave a dull, dirty appearance on your pool liner, a bathtub ring, or dark and discolored areas.

    Chemical loss occurs too when you close a dirty pool. The winter chemicals that you add will become used up as they attack organic material left in the pool. Algaecide doesn't know the difference between algae and leaves, it's all the same - and it consumes your chemicals that are meant to last the entire season, leaving none to battle algae as the pool warms up in pre-opening spring water temperatures.

    So, vacuum, brush and skim the pool, or run the pool cleaner for an extra long cycle. I like to also clean the pool deck off with buckets of pool water, to prevent leaves from blowing in the pool as we continue on to other pool closing tasks. And, right before putting the cover on the pool, run the leaf rake (skim net) around the pool to pull out any leaves that have blown into the pool.


    If you are using a mesh safety cover, lower the water level about a foot (12 inches) below the skimmer opening. If you are using a floating solid winter cover with water bags, lower it about 4 inches below the skimmer.

    Our inground pool kits commonly have a dedicated main drain line, running all the way back to the pump, with a 3-way valve to control the flow. To pump the water below the skimmer, close off the skimmer valve, and pump only from the main drain to drop the water below the skimmer opening.

    After backwashing your filter for 15 minutes or so, shut off the pump and switch the filter valve (multiport) to the waste position, and continue to lower the water. When the water gets below the  skimmer, you can crack the valve open, and suck the water out of the skimmer line, closing it before it draws too much air into the pump, which could cause the pump to lose prime.

    If you do not have a separate main drain valve, you can set-up a vacuum hose/head into the skimmer to pump the pool below the skimmer. Use a hose adapter or duct tape around the hose to get a good seal into the skimmer. If it still draws air, you can keep a garden hose running into the skimmer to keep it from sucking air.

    If you have a cartridge filter, and therefore no multiport valve, you may need to use a submersible pump, like a pool cover pump, or a sump pump, to lower the water level. It's best to use a fast pump, and not a slow siphon, so that the pool doesn't get dirty again while you are lowering the water level.


    Bob just recently wrote a post on how to use the Cyclone blower to blow the water out of the underground pipes. You can also use a 5 hp Shop-Vac to blow the lines out, (reversing the hose) but this may not have a high enough CFM rating to blow out a main drain, because many wet/dry vacs allow air to blow out around the top when there is too much resistance.

    You can also use a small air compressor, but keep the pressure low, under 20 psi. You can blow air from the skimmers, through the filter system, and back to the pool returns, or you can blow air from the pump in both directions, back to the pool skimmers and drain, and through the pump to the pool returns. Blow air in every direction, until you are confident that most of the water is removed. A little bit of water deep underground won't usually cause you any problems, as long as the pipes aren't full of water.

    While blowing air through the returns, you should remove the drain plugs on the pump, filter, heater, etc - to allow the water to blow out. Store the drain plugs in a safe location, like the pump basket, so you can find them easily next spring.

    Non-toxic pool antifreeze can be added to pipes as added insurance against leaking plugs, or if you do not blow out the lines, you can pour enough pool antifreeze into the underground pipes to prevent freeze damage. do not use antifreeze in the pool equipment though, blow these out or make sure that they have drained completely.


    Plugging the skimmer and return lines keeps water from getting back into the pipes once they are winterized. You can use rubber expansion plugs, aka Freeze Plugs, of the proper size. Push them in and tighten the wing nut to make a good seal. Or, you can use the threaded plastic plug with o-ring. Put some Teflon tape on the threads to help seal and a small amount of pool lube on the o-ring to prevent dry rot.

    If your return lines are still under water when you blow the lines, you will plug them as they are bubbling. You will first see the return closest to the pump bubble first, and after plugging it, you will see the other return start to blow. If you have a cleaner line for a booster pump type of pool cleaner, these will usually bubble last, and very strongly. If there is too much air to plug it while bubbling, have a helper shut off the blower at the same time as you start to plug the line.

    Main drains aren't commonly plugged - unless you want to dive down there and plug it! Just kidding - the trick for a main drain is to close off a positive sealing valve (like a Jandy valve) on the pipe as the air is bubbling out of the main drain. While the air is bubbling strong from the drain, turn the main drain valve quickly to close off the drain. A positive sealing valve will hold the water out of the pipe, like a finger on the end of a straw.


    After you suck out or blow out the skimmer, or treat with antifreeze, and plug the skimmer - there is one more step to winterize the skimmers. Water can splash into the skimmer pot from the pool, or can drip into the skimmer from rain and snow melt. When this water freezes, it puts enough outward pressure on the skimmer walls to crack the skimmer.

    To avoid this, you have four options. You could pour some pool antifreeze (not car antifreeze!) into the skimmer, on top of the plug - or, you can use a Gizmo, which is a combination skimmer plug and ice absorption cylinder - or, you can halfway fill a clean quart or gallon bottle with pea gravel or antifreeze, and drop it in the skimmer - or, you can use an Aquador skimmer closure, which prevents water from entering the skimmer on the pool side, and a piece of heavy plastic under the skimmer lid to keep out rain water.


    In addition to draining the aboveground pool equipment completely, there are some other maintenance tasks to be done on your pool equipment.

    Filters: DE filter grids should be removed and hosed off completely, to remove all traces of DE powder from the grids, which will dry hard onto the grids and clog the fabric. Cartridge filters should also be cleaned as thoroughly as possible; I recommend using our cartridge filter cleaner chemical to soak them before cleaning, to remove oils and minerals. Sand filters should be backwashed thoroughly and also cleaned with a sand filter cleaner to remove oils and gunk from the sand bed.

    Pumps: Lubricate the pump lid o-ring with Teflon lube, and leave the drain plugs out, storing them inside the pump basket with the filter pressure gauge and other drain plugs.

    Heaters: Shut off the gas, turn off the gas valve and disconnect the pressure switch, to allow water to drain from the siphon loop (Jandy heaters). Heat pumps should have the unions disconnected and then be tipped slightly to allow the water to drain out.

    Chlorinators: Remove any unused chlorine tablets, and allow them to dry before putting them back into a chlorine bucket. Better yet, put them in a heavy duty plastic bag, like a Ziploc freezer bag, and place them on top of the chlorine bucket. Lubricate the chlorinator lid with Teflon lube.

    Salt Cells: Remove your salt cell for storage inside during winter and wrap the electrode terminals in a plastic bag to protect them from the elements. Cover the control panel as well, to shield it from rain and snow.

    Valves: Multiport valves should be left in an up position, with the handle popped up between any two settings. do not place the valve  in the closed position. Push pull filter valves should be left in a halfway position, after lubricating the plunger o-rings with Teflon lube. Jandy valves can be left in any position, but I tend to leave them open, except for the main drain valve, which should be closed. Remove the valve handle to prevent it from being opened by accident, by person or animal, or tighten down the lock nut securely.


    A winter chemical kit, aka closing kit is a good way to get all the chemicals you need in one box, and is the only way to get the non-chlorine winter floater, highly recommended for vinyl liner pools.

    Using a chlorine floater is risky, if it flips over, or comes to rest on a step or swimout, or just sits up against one area for a long time, it will bleach even the strongest liners. If you insist on using a chlorine floater, tie it off with string on both sides of the pool, so that it remains in the middle of the deep end area.

    As a minimum, you should use one quart of very good algaecide (Poly 60) for every 20,000 gallons. Use more if your pool cover is in bad shape, or if you have a mesh safety cover, which lets in dust and sunlight. Just pour the algaecide around the pool. A non-chlorine floater is also a good idea to keep a sanitizer in the water during winter.

    If you use a Stain  & Scale treatment, it is recommended to add this to the pool before lowering the water, so that it is mixed very well in the pool. The algaecide can be added after lowering the water, to increase it's effectiveness.

    Do not add shock and algaecide to the pool at the same time, the shock can break apart the polymer bonds, and render it useless. Shock the pool days before closing, and then add the algaecide during closing. Or, shock the pool during closing, and then add the algaecide a few weeks later, by lifting up the corners of the cover and squirting it in under the cover. You could also wait until early spring (March-April) to add the algaecide.


    You're almost done! Before installing the pool cover, run the skimmer net around the pool to remove any leaves that have blown in the pool. Grab a helper for this step, it's almost impossible to put on a large pool cover by yourself.

    Safety covers are the best type of winter pool cover to use, and if you really want to protect  your pool, install a Solid Safety Cover (without drain panels) will keep out all sunlight, and all contaminants that wash in from rain and snow melt.

    Solid winter covers, held in place with water bags, also block out sun and debris, but are fairly fragile, and require more maintenance during winter and during spring removal. And, if they rip or develop holes during the winter, which is probable one day, it will spill concentrated gunk into your pool, creating a nightmarish pool clean-up. Keeping it clean and dry is the best way to prevent this from happening. That, and replacing it when the time comes, instead of trying to get one-more-year out of it.

    If you do have a solid pool cover, and you have a lot of large trees around the pool, a Leaf Net is the best way to deal with the leaves. Lay it on top of your solid cover when you close the pool, and then after all the leaves have fallen, clean-up the area around the pool and remove the leaf net, removing all of the leaves in one fell swoop. It's not recommend to keep a Leaf Net on the pool all winter long, but store it after the leaves have fallen - they will last much longer if they aren't allowed to freeze onto the pool cover all winter long.


    Last step is easy - shut off the power at the breaker and at the time clock. Remove the timer dogs from the time clock, just in case someone turns the breaker back on. Breaker boxes have a tab at the bottom to accept a padlock, if you want added insurance against the pump turning on without water to pump - which could cause irreversible damage.

    >>> The first time you close your pool, it may take you 3-4 hours, but after practicing a few years, you will cut that time in half. If you have any questions, any questions at all - please feel free to call or email us. If it's a complicated question, send along a few digital pictures to illustrate your winterizing questions.

    I guarantee that you can close your own pool - even if you didn't build your own pool, you can winterize it yourself, and save a chunk of money every time!

    Chris Low
    SPP Pool Expert

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