How to Clean an Algae Stained Concrete Pool


It’s been a long cold winter, my inground pool is a mess. A huge branch from a tree nearby snapped and fell tearing the cover and exposing it to the winter months. Our concrete pool spent most of the last 4 months sitting with no cover.  It has happened before and I learned how to get the algae stained pool cleaned and opened for Memorial Day. How to Clean an Algae Stained Concrete Pool?

  1. Pump the pool out,
  2. Remove all debris making sure that all organic material is cleaned out.
  3. Apply Muriatic Acid safely to the walls and bottom.
  4. Rinse off completely.
  5. Fill Pool, Shock,
  6. add Algaecide & Clarifier,
  7. Stabilize Alkalinity, PH & Chlorine
  8. Run Filter

For the longest time, the cover on our old pool lasted through some big snowstorms. This year, it gave in. I know what to expect when I pump the water out of the pool. A Green, Black murky swamp that just last season we were swimming in.

Black Algae on Concrete

 

My family owns an old concrete Sylvan inground pool that has been around for more than 50 years. It has some odd dimensions that are not used anymore. The pool is 10 feet deep at one end and 4 feet deep at the shallow end.  The length is around 38 feet long and 15 feet wide. It a bear of a pool and can be a lot of work to open and close along with regular maintenance to keep up with. This past winter we lost the Cover It has never been worse!

Because of the pool being in the proximity of the woods we have had some major problems with trees and all they do to interrupt the pool environment. We have whittled away a lot of them to let the sun come through that increased the temperatures. It also kept bug leaves and debris from finding their way into the pool every time the wind blew. It’s worked but not completely.

The pool has different dimensions because of its age so covers are difficult to order and have to be made special sized and special ordered. Because we lost the cover, the biggest and most problematic job about operating an old-style monster size concrete pool is Opening it up. Especially if the pool’s cover had a problem during the harsh winter months here in Pennsylvania where the weather conditions can get really bad.

The Pool lost its cover in December 2018 after Christmas. It will be needing some extra work this year. After the ice thaws, I will need to pump out the pool and start cleaning the black, brown, and green algae that have stained the walls and bottom, right after I shovel the mess that I know is there from the long winter. I have been here before.

 

 Draining a Concrete Pool

In this case, the branches and leaves from trees are at the bottom. I know because there was a big storm after Christmas and the branches from the tree in the back of the pool are what tore through the cover and sank to the bottom. The pool now is a black murky swampy mess. Can I clean it maybe but not without draining the pool. The Pool from Hell!

I know there is a lot of garbage at the bottom of the pool. In this case, it would take more time and money to try and clean the stuff at the bottom while trying to save the cost of refilling it with fresh water.

All pools are different. There are things to consider about your situation. that might be different than mine. How big is your pool and how much money will it cost to refill it. Water is not inexpensive depending on where you are in the world.

Where I  live in the world, there is a surcharge that is tacked onto your water bill if you go over the normal rate of use.  How much that is and what the surcharge is most likely different all over the State.

As far as other countries, I have no clue. You need to examine you, Utility Bill, the next time you get your hands on it. It’s good to know. if it is too much money to empty your pool and you want to save it and you didn’t have a pool cover on it the last six winter months, then you got some work to do. My pool holds 48,000 gallons. It’s a huge old pool. It cost a lot of money not only to fill it but keep it filled for the season. I am going to pump out the water and make it a little easier on myself. But if you want to salvage the pool water then you got some work to do.

Draining your inground pool after losing your cover and leaving the water exposed to the elements all winter is the Best Choice for a pool owner to make. It gives the pool owner the access and opportunity to get inside the pool and get things going. You make valuable inspections that may be urgent and need your attention.

Once the water is out you can see what’s on the bottom, and assess the damages that have happened from over the winter. You can get an idea of other damage that you might have not known about. Cracks caused by stress or problems with the drain plug cover are important things, that if not addressed will get worse.

You’ll also be able to see if water from the outside yard is making its way in. That is a disaster waiting to happen. You can get the water out as fast as possible so you can get down to the real work, cleaning the acid stains and organic material that have to come out so you can get your pool back to the same place it was last season.

A good place to start is to rent a 3″ Trash Pump from a Home Depot or another rental store. A 3″ trash pump will take an inground pool down in a few hours depending on how big. You can use the filter pump that is set to vacuum in conjunction with it but I really think that it’s the fastest way to “get er done” These pumps can be rented fairly cheap and by the hour.

Another way take the whole pool down with the pool pump by simply using Waste on The Selector Valve on your filtering system and emptying the pool through the Backwash Hose. Once you get as low as possible you can use a Puddle Pump that can take the water down in the drain at the deep part of the pool to a fraction of an inch. MyWaterEarth&Sky has one of the better Puddle Pumps on our Recommended Products page. Jump over and take a look. If you have a pool there are a hundred reasons to own a Puddle Pump like this one Tsurumi HSZ2.4S; Float Operated semi-Vortex Submersible Trash Pump w/Agitator, 1/2hp, 115V, 2″ Discharge

Start early to get it open by Memorial Day weekend. Do This: 

  • Remove the branches, leaves, and trash that are floating on top and at the bottom of the pool. Start where you can see. Work in a grid across the bottom of the pool and get everything. The more you get out the more you’ll save on the use of chemicals in the next process.
  • Open the Inlet Covers and blow any debris that is in the boxes into the pool. Make sure they are clean. Put the baskets back in and the Covers back on.
  • Clean the inside of the pool first. Make sure you collect and remove any Organic Material that is unseen on the bottom of the pool. Use a Soft Plastic Rake or Use a Leaf Bagger first that has a long pole and that is heavy enough to drag along the bottom capturing branches and leaves. Everything has to be taken out of the pool for your next step which is to chemically treat the water in the pool. If you leave any organic matter in the pool that material, no matter how small, will suck up the chemical’s active ingredients you are using and will triple the cost and amount you are using.  After you are done with cleaning the debris from the pool now it’s time to clean the mess that is around the pool.
  • If you let it go,  as soon as the weather warms a few degrees, that organic material that you left from cleaning the inside of the pool will dry and stain your walkway or patio blocks that surround the pool area. Those new stains will be harder to remove than the stains you fight on the inside of your pool. So Get to it.

The equipment you’ll need:

Trash pump this size Capable of moving up to 400 GPM and solids up to 1.5″. It can be rented for 4hours at a time or the whole weekend.  While you there pick up a Plastic Gardening Waterer

Watering Can-2 1/5 gallon watering can to use with the Muriatic Acid.

Eye Protection-protect you from Chemical splash-You will absolutely need these. For a couple of dollars, you can save yourself from blindness. buy them

Chemical Gloves-Versatile chemical protection glove for when you need to be protected from hazardous materials. Made of a high-performance nitrile compound that provides an outstanding combination of chemical resistance and strength.

Muriatic Acid- This chemical will clean the walls and the floor of the swimming pool. The less expensive Muriatic Acid has more fumes and is more dangerous to handle. Directions for working with Muriatic Acid:
Wear protective clothing, rubber gloves, and plastic safety glasses while using. To etch or clean concrete and masonry or metal:
Dilute to desired strength by adding acid carefully to water, avoid splashing.
Start with a highly diluted mixture and strengthen gradually (1 part acid to 20 parts water).
Apply solution. Bubbling indicates the solution is strong enough.
Flush thoroughly with clean water and immediately after cleaning or etching is complete.

Masonry can be very alkaline, which makes for poor adhesion of paints, etc. Washing masonry with muriatic acid neutralizes the alkalinity, leaving it in optimal condition to accept paints and other coatings. When cleaning masonry with muriatic acid, a powdery residue is left on the surface. Once that residue is rinsed off, you are left with a very clean, coating friendly surface. 

Even though Muriatic Acid is safe when used properly, you need to use caution. The new type of Muriatic Acid has low Fumes  Make sure that it says Green or Low Fumes on the label. Muriatic acid and its fumes are extremely destructive. They can damage or discolor most materials on contact, including metal, wood, natural stone, masonry, fabrics, and vegetation. Always use caution and test before using it. Wear protective clothing, rubber, gloves and plastic safety glasses when using this product. Avoid splashing. If the container shows signs of deterioration, dispose of properly.

 

Hydrostatic Valve

 

Newer pools are lighter using Fiberglass and other materials that don’t use heavy framing inside the material that holds everything together. If you empty your pool there is the question of whether or not the ground underneath your pool could float or push the pool upwards cracking, buckling, or splitting the whole pool in half destroying it.

There are other issues that leaving your pool empty could cause movement, where the pavement, patio cement, concrete block, or stones are destroyed by a small movement of the empty pool, pushed up by groundwater. Hopefully, your pool was elevated from the surrounding areas that should be lower than the pool structure. You can easily notice this. step back and look at the whole area. This is what you should see.

Another safety mechanism in an Inground pool that not too many people know or talk about is the Hydrostatic Relief Plug  that is normally found in the center of the pool, sometimes referred to as “Hydrostats.”  While typically plastered in place, they are threaded into a piece of piping that runs along the floor of the pool, leading into the gravel pit beneath the pool. They may be more than one. One in the shallow end and one in the mid-level and deep end of the pool. To completely drain the pool using the Hydrostatic Valve.

My Hydrostatic Relief Plug is inside the Drain Pot at the deepest part of the pool. In the 30 years, I have been performing maintenance on my swimming pool, I have used this relief plug many times and never had a problem. Every 5 years or so we have painted and patched the pool and even resurfaced the entire pool keeping it closed for long periods of time, If you are leaving your pool empty for any length of time, Do This:

  • Locate the Hydrostatic Relief Valve
  • Normally under the main drain pot that is covered by the Plastic Drain Cover in the middle and deepest area of the pool.
  • Remove the Drain Cover-Usually held in by 2 or more stainless steel screws. 
  • Chip away any paint or cement whatever the pool was made like Gunite or Shotcrete construction material that is sprayed on framing to make the shape of the pool. 
  • You might have some collection of paint or stones inside the Drain Pot. Scoop that stuff out and you’ll see or feel big (again it all depends on the size of your pool) 1 ” -1 1/2 “Plug with a square head on top. I got a ratchet on mine and with some healthy persuasion, it moved. 
  • Lefty Lucy-Righty Tighty and that bugger came out. 
  • When I put it back in I cleaned and used Teflon tape on the threads. 

How Hydrostatic Relief Plugs work is that groundwater under great pressure underneath the pool might and in some cases do lift the pool no matter how heavy the pool is. The opening in the pool gives that water normally groundwater under high pressure somewhere to go relieving the pressure by entering the empty pool.

So in theory you can keep your pool empty for long periods of time if these valves are working and unobstructed.

 

Muriatic Acid Pool Cleaning

 

  • After the pool is pumped completely as far as it can go with the 3″ Trash Pump and all organic material is removed shut down the garden hose.
  • Remove any tools like the wheelbarrow rakes or Leaf Baskets. All that is left is green and Black Algae stained walls and bottom.
  • Let the walls in the pool dry a little more. This will give the Muriatic chemical a better activation when you ally it to the walls.
  • Keep the garden hose connected where you can get to it just in case you have a problem with splashin the Muriatic Acid on your skin. Always use this chemical saftley. Muriatisc Acid
  • Always wear Gloves and Protective Chemical rated gloves. Use your brain and this stuff realyy will work!!
  • Always Add Acid to Water/never Water to Acid 
  • Fill the Watering/Springling Can up with 2 parts water and 1 part Muriatic Acid. 
  • Stay on the edge of the pool with the wind at your back (this will keep any fumes away from you) Walk the perimeter of the pool using the diluted Chemical in the Sprinkling Can and pour the solution at the top of the wall. It will cover the whole wall from top to bottom covering it.
  • It will turn a yellowish color foam and smell  pungent like vinegar. If it doesn’t foam and turn yeallow it is not strong enough. Try a stronger dilution like 1 to 1.  Always pouring Acid into Water Never Water into Acid. It’s just a little safer rule of thumb. That goes for any type of Acid.
  • Assuming that the Acid turns the algae to yellow, move around the paremeter of the pool, soaking the wall from the top and covering the entire area. Leave it sit until you can noticeable see that the foaming has stopped and the acid is no longer activating on the wall. Then take the hose and rinse the Muriatic Acid from the wall and whatever rolled acrossed the bottom towards the drain in the deep end. You can add more of the acid to troubled spots on the bottom of the pool using full strength.
  • Do Not Go In The Pool While You Are Using Muriatic Acid To Clean The Stains on The Pool Walls Or On the Pool Bottom. Even though the new Muriatic Acid is lesser strength than the older stuff that I used, working in Water Treatment facilities, It’s still acid. It still reacts with water to form a gas that you can see in the air. It will still react with Humidity in the air. So using it is needs to be done with caution. Like chlorine it can take your breath away. If you are in a Confined Space, which is a space that is over your head like the deep end of a swimming pool, you are in a hole.

Gases from Chlorine, Bleach, Cleaners, Epoxy or Rubber Base Pool Paint and Muriatic Acid and other chemicals found in Pool Supplies can react with water or humidity (which is water in air) and change to a gaseous form that is heavier in nature than oxygen.  if you are in a lower end of a pool then you are in a  Confined Space. I have seen this. Vapor or gas sinks and pushes the oxygen up leaving you in a dangerous position. When you use products like pool chemicals be careful.

 After the pool is emptied cleaned and acid washed it’s time to refill it and put the pump and filtering system back together. 

 

How to Start Up a Pool For the First Time

  1. Start to Refill pool to correct level
  2. Adjust Alkalinity-1st- Nothing works unless this part of the pool’s chemistry is stable.
  3. Adjust PH-2nd- When adding Alkalinity and PH Adjusting Chemicals, try and deliver the powder evenly distributed around the perimeter of the pool.
  4. Add Shock-3rd -Broadcast the Shock the same way evenly distribute the chemical around the perimeter of the pool. Closer to the walls where the Shock will come in contact with algae-covered walls. This will kill off some tougher to scrub walls that are thicker with algae.
  5. Open Inlet Ports-Start the Pool Pump and set the handle on a filter to Recirculate pool water.
  6. Add Clarifier-4th- You might have read not mix pool chemicals with water- Mixing Clarifier is a Better way to apply to your pool’s surface water. So mx a bottle with a bucket of pool water and walk around the perimeter of the pool and distribute the mixture evenly a foot or two of the pool’s walls.
  7. Vacuum to waste -5th- At first the muck and trash you vacuum from the bottom of the pool will be thick just like you would expect it to. Bypass that trash away from your filter and swimming pool out your backwash hose and away from
  8. Filter pool water-6th-Make sure your pressure gauge is working and check this often. 
  9. Add Algaecide Inhibitor-7th- Mix the bottle of Algaecide in a bucket of water and walk the perimeter of your pool adding the chemical evenly distributing the contents. Take a skimmer and stir the water in the pool to mix it all up.
  10. Repeat any steps that are needed. 

Draining your inground pool after losing your cover and leaving the water exposed to the elements all winter is the Best Choice for a pool owner to make. It gives the pool owner the access and opportunity to get inside the pool and get things going. You make valuable inspections that may be urgent and need your attention.

Once the water is out you can see what’s on the bottom, and assess the damages that have happened from over the winter. You can get an idea of other damage that you might have not known about. Cracks caused by stress or problems with the drain plug cover are important things, that if not addressed will get worse.

You’ll also be able to see if water from the outside yard is making its way in. That is a disaster waiting to happen. You can get the water out as fast as possible so you can get down to the real work, cleaning the acid stains and organic material that have to come out so you can get your pool back to the same place it was last season.

A good place to start is to rent a 3″ Trash Pump from a Home Depot or another rental store. A 3″ trash pump will take an inground pool down in a few hours depending on how big. You can use the filter pump that is set to vacuum in conjunction with it but I really think that it’s the fastest way to “get er done” These pumps can be rented fairly cheap and by the hour.

Another way take the whole pool down with the pool pump by simply using Waste on The Selector Valve on your filtering system and emptying the pool through the Backwash Hose. Once you get as low as possible you can use a Puddle Pump that can take the water down in the drain at the deep part of the pool to a fraction of an inch.

 

Continue with my 10 steps for How To Open Your Inground Swimming Pool In Time For Memorial Day that is written above. Make sure that any residue left at the bottom of the pool is taken out either by the Trash Pump or even by Bucket. For about 50 or 60 dollars plus the cost of renting the Trash Pump, you can get your pool back to normal with plenty of time left before the season starts.

After the pool is empties cleaned and acid washed it’s time to refill it and put the pump and filtering system back together. Oh, Don’t forget, your going to need another Pool Cover so you won’t get stuck with this mess next year.

 

Related Questions

What causes Brown Stains in a Pool.? There are a couple different reason that you see brown color in a swimming pool. One reason is Brown Algae. The second reason could be high iron content. If your water supply is from a Well it’s likely it’s high Iron concentration. If Not Shock your pool.

How Much Water in Your Pool Do You Drain For The Winter? The standard is to drain your pool below the skimmer levels so that you can clean out the plumbing system to avoid frozen, burst lines during the winter. In an Inground Pool That might Mean a Little more draining.

 How long can you keep chlorine tablets? Properly stored chlorine tablets should last three to five years. The storage site should be cool, dry and well-ventilated, such as in a basement

Jim has over 30 years in the Water/Wastewater and Water Filtration Consulting Business. He has written over 300 articles on the World-Wide-Water Situation

JimGalloway

Author/Editor, MyWaterEarth&Sky

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