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How to Acid Wash a Pool

When you choose to acid wash your pool, you are also choosing to damage the pool’s surface. This devil’s bargain trades the longevity of the pool’s surface for the extra cleaning power of acid. These acids come in two primary forms, muriatic and ascorbic. If given the chance, muriatic acid will rapidly disintegrate and destroy each of the pool surfaces. Even brief exposure will reduce those surface’s lifespans. Ascorbic acid (vitamin c) only has about a tenth of the acidity, but it is still powerful enough to damage any pool that makes contact with a concentrated dose.

You might be asking, “If that’s true, why would anyone want to perform an acid wash? Why not simply perform a pool shock (chlorine shock) and scrub the pool?” The answer is that acid washing is the single most powerful cleaning option in the pool owner’s toolbelt. If you have stubborn stains or a deep-rooted black algae contamination, a pool shock might be too weak to eradicate those issues.

An acid wash is caustic enough to deteriorate plaster, so biological life that’s fully doused in one of these acids won’t stand a chance. That isn’t to say that acid washes always work. Black algae spores can penetrate porous plaster surfaces. If the acid wash fails, the only other option is to seal away the problem behind a new layer of plaster. Replastering costs thousands, so that’s not the ideal option for most people.

What Types of Pools Can Be Acid Washed?

Since acid washing can easily do thousands of dollars of damage to your pool, you’ll need to know how to treat your pool type without damaging it. Acid washing is not a one size fits all.

  • Concrete: Gunite and shotcrete are the toughest, and can be acid washed with muriatic acid.
  • Fiberglass: Muriatic acid will destroy the gel coating. Can be acid washed with ascorbic acid.
  • Vinyl: Never acid wash. You will destroy your vinyl liners.

Draining Water Can Damage Fiberglass Pools

Inground pools must be strong enough to withstand the constant crushing force of the ground outside of them. Fiberglass pools are susceptible to compressive force. The water helps support the fiberglass structure by balancing out compressive force of the dirt and gravel with the fluid pressure exerted by the thousands of gallons of water that the pools’ hold. If the pool walls are not professionally reinforced before draining, the pool can distort and even crack. For this reason, we recommend performing a no-drain acid wash on fiberglass pools.

Acid Safety

Your health is more important than your pool, so we ask that you pay close attention.

You might damage your pool, lungs, skin, and potential accidents with the acid could lead to lethal consequences. 

Protective gear must be worn and appropriate safety precautions must be taken. Here are our guidelines, but we recommend doing further research offsite to protect yourself.

Wear Appropriate Safety Gear

  • Safety goggles respirator mask – Must be rated for acid
  • Long-sleeved shirt
  • Elbow-length chemical-resistant gloves
  • Pants
  • Closed-toe shoes

Protective Practices

  • Avoid acid splashes
  • Dilute acid in the right order
  • Don’t acid wash your pool on a windy day
  • Don’t rush the job
  • Follow the manufacturer’s instructions
  • Have a wastewater disposal plan
  • Keep kids and pets away
  • Keep the pool clear

Step-by-Step Instructions for Acid Washing a Pool

By now, we are assuming that you have read the warnings, know how to work safely with these acids, and put on your protective gear. If you have, you are probably ready to acid wash your pool.

Equipment Needed

  • Submersible pump – It should have a long cord or an extension cord
  • Acid – Ascorbic Acid (Fiberglass) or Muriatic Acid (Concrete)
  • Garden hose – That can reach all areas of the pool
  • Soda ash – 2 Pounds of ash per 1 gallon of acid.
  • Long-handled acid brush
  • Tall rubber boots
  • Watering can

While the task is simple, we recommend reading through all of these steps. Knowing all of the steps ahead of time will prevent unnecessary deterioration of the plaster.

Step 1: Drain and Scrub Your Pool

Unless you are performing a no-drain acid wash, which is a different guide, you should start an acid wash by completely draining the pool. 

As you drain the pool, you should take advantage of the wet walls and try to scrub the muck off of the walls. We know from experience that all of that muck is a lot more difficult to remove when dry. This scrubbing will help to remove the slimey coating and shell-like armor that keeps chlorine from killing black algae. You should take advantage of those soaked walls and scrub the pool while it is draining.

Final Warning – Fiberglass pools need to be professionally reinforced before draining.

Optional Step: Pressure Wash

Pressure washing the walls can significantly reduce how much acid you’ll need to clean up the pool walls and floor. If you have a pressure washer handy or don’t mind the cost of a rental, we highly recommend this optional step.

Step 2: Turn Valves to Plug the Drain

The acidic water shouldn’t drain into the groundwater. For this reason, after you have drained the pool, turn the valve(s) to reseal the drain.

Step 3: Set up a Submersible Pump

We also don’t want acidic water to pool up at the lowest point of the pool. If it does, the acid will quickly start to deteriorate the plaster. To prevent this, set up a submersible pump at the lowest point to continually pump out that water. Be careful where you pump the acid.

Step 4: Dilute Acid with Water

The muriatic acid should be diluted with water. We recommend using 30% muriatic acid and 70% water. Professionals will sometimes use a solution that’s a bit stronger, but we recommend that newbies stick to 30% to reduce the risk of hurting themselves and their pools. Acid washing already damages plaster, and increasing the acidity will increase the damage.

Add this mixture into a watering can.

Step 5: Spray One Wall and the Floor with a Hose

Use a hose to spray water onto the section wall you are prepared to acid wash. You should also spray the floor near the wall because it will add a bit of protection to the floor. 

We also recommend keeping the water running throughout this process because the acid should never rest upon the wall for more than 30 seconds. Turning the water off and on will slow your ability to wash the acid away.

Step 6: Pour Diluted Acid Solution onto Small Sections of Wall

If you acid wash the pool yourself, the amount of acid wash you need will generally cost about $.06 per square foot of the pool’s walls. Within the United States, the labor will cost an average of $.40 to $.48 per square foot. Using this information, a 10x20x5 might cost $384 in labor and $48 in supplies.

Step 7: QUICKLY Scrub the Walls and Rinse

Once applied, scrub the wall with the acid brush for 30 seconds before quickly washing the acid away. Try to be consistent and methodical as you scrub the surfaces so the ending result will be uniform.

Step 8: Neutralize the Pool of Acid with the Soda Ash

Each gallon of acid that you use will need to be countered with two pounds of soda ash. Add that soda ash to the puddle that naturally pools as the water runs down the walls and floor.

Questions and Answers

What Type of Algae and Stains Can Acid Washing Remove?

We can use acid wash treatments to remove all types of stains and algae. It can even effectively remove the infamous pool nemesis, black algae. That said, it isn’t a perfect solution. Concrete is porous and can harbor algae cells that only replastering can eliminate.

When Should You Acid Wash Your Pool?

Acid washing deteriorates the plaster, so it should only be performed roughly once every 5 to 7 years. Visually speaking, you should acid wash your pool walls when the walls and floor are looking gross with algae and mineral deposits and standard cleaning is not restoring the walls to a clean look.

How often should a pool be acid washed?

Concrete pools and fiberglass pools should be acid washed roughly once every 5 to 7 years. That isn’t a hard rule. However, by that time, there are usually enough organic stains and mineral buildup to warrant an acid wash.

How much does it cost to do an acid wash pool?

If you acid wash the pool yourself, the amount of acid you need will generally cost about $.06 per square foot. Within the United States, the labor costs an average of $.40 to $.48 a square foot. Using this information, a 10x20x5 might cost $384 in labor and $48 in supplies.

Is it safe to acid wash a pool?

No, it is not safe to acid wash a pool. We aren’t saying you shouldn’t acid wash the pool. However, if you do, you should read labels and safety information regarding the products and their use. Muriatic acid fumes are poisonous and direct contact with skin or eyes can result in chemical burns.

How long does acid washing a pool take?

If you haven’t acid washed a pool before, it will likely take two to three days for an individual to acid wash a pool.

Can you swim in the pool after an acid wash?

If you drain the pool to perform the acid wash, the muriatic acid should evaporate before you have a chance to refill the pool. If the muriatic acid has evaporated, the pool will be safe for immediate use.

Does muriatic acid remove pool stains?

Yes, muriatic acid, also called hydrochloric acid or chlorine, is the common recommendation to remove most organic stains.

What is the benefit of acid washing a pool?

Acid washing a pool removes algae, calcium scaling, and stains from the surface of your pool. When these contaminants are removed, chemical consumption is reduced.

How do I get stains off the bottom of my pool?

The method needed to remove stains from the bottom of your pool will depend upon the composition of that stain. In most cases, a mixture of chlorine granules and scrubbing will do the trick.

Why does the bottom of my pool look dirty?

If it is dirt, there might be a problem with your filtration system. The filtration system might be ineffective due to inadequate capabilities, or it might need to be backwashed. If it only looks dirty, it might be a metallic stain or some form of algae.

Is muriatic acid the same as hydrochloric acid?

Yes, muriatic acid and hydrochloric acid are the same molecules.

Does muriatic acid remove pool stains?

Yes, muriatic acid can remove many types of pool stains. However, it can’t remove everything. Muriatic acid can remove organic stains, but metallic stains will need to be treated with a sequestering agent.

Can you acid wash a pool in the rain?

You can acid wash in light rain, but you should wait till later if the rainfall is more substantial.

Can you acid wash a PebbleTec pool?

Yes, you can acid wash a PebbleTec pool.

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