Pool acid washing is also called drain and clean pool servicing. This becomes necessary when winterizing processes are not done efficiently and the pool has turned into a black lagoon. Also, if the water in the pool has stagnated for a prolonged time such that algae has overwhelmed the pool and has taken over with some leaves and debris to add to it.
One general guideline in the determination of the need for a pool acid washing is that if the bottom of the shallow end floor can still be visualized, then the pool can probably be brought “back to life” with chemical compounds, cleaning, and proper filtering. Inversely, if the floor of the pool cannot be visualized, the number of chemicals and manual labor required to clean the pool may be more than what pool acid washing offers, and this process takes longer as well. Another thing to remember is that extensive algae blooms or expansive pool neglect will often leave stains on plastered pools and make acid washing anticipated necessary.
Technically, the definition of pool acid washing is the stripping of a thin layer of pool plaster thus focusing on exposing renewed plaster underneath. It is therefore not advised to practice acid washing as annual maintenance, thereby accelerating a pool’s replastering needs. Most plaster coats, sometimes referred to as a whitecoat, are often with an excess of about half an inch, making thorough acid washing recommended only every 5 years.
Pool acid washing may also be an option not just due to a pool’s swampy conditions but only to bring out a much brighter, fresher finish. Often, pool acid washing can improve the aesthetics from mineral stains and deposits, chlorine stains, and dirt stains, and acid washing can also improve plastered fountains.
If a pool has had an extensive history of algae blooms or if a pool grows algae at a very fast rate or with relative ease, changing the water and trying pool acid washing the surfaces may offer a solution when every option has been exhausted. This may be the remaining option to have an algae-free summer in conjunction with having a recommended filtering medium.
A word of caution must be said about using muriatic acid in pools as this substance is highly toxic. There are existing alternatives though to muriatic acid that are much less hazardous to work with. Remember that not just anybody can perform acid washing and so all personnel involved must be trained in safety going about a drained pool, wearing personal protective equipment (commonly, breathing masks suitable for acids) and clothing. In addition, acid-water waste must be neutralized with a basic agent that can increase pH according to environmental regulation standards before it is discarded to a safe location.
Once the decision to drain and clean a pool has been made, the hydrostatic relief plugs of the pool should be removed as soon as possible, together with the pumping of the pool water to a distant spot or a storm drain. This should be done to avoid seepage of this volume of liquid underneath the pool. If a pool sits in areas that are geologically depressed, with recent heavy rainfall, or with a high-water table, extra caution must be done to manage hydrostatic pressure under the pool during pool acid washing-related procedures.
Pool owners may also have to check with their local water authorities for regulations regarding wastewater disposals in the area. When pumping across the soil, make sure to move the hose regularly as needed to avoid soil erosion and oversaturation.
Pool Acid Washing Supplies
To properly prepare for the pool acid washing procedure, generally anticipate these needed supplies and materials:
- A suitable garden hose that will reach pool areas easily, preferably with also a nozzle
- A flower watering can (for pouring acid)
- Pump and discharge hose (for draining the pool and wastewater)
- Around 10 to 20 gallons of acid (largely depending on the size of the pool and staining severity)
- Soda ash with a ratio of 1:2 acid to soda ratio in gallons
- Protective equipment and clothing such as safety goggles and acid masks
- Tools such as screwdriver, chisel, and pliers (to remove plugs and drains)
How to Perform Pool Acid Washing on a Concrete Pool
Follow the subsequent steps to perform acid washing on concrete pools.
- Drain and Clean the Pool
Most pool water can be drained with a filter pump warranting that the pool has a main drain and a multiport filter valve. This may not get all the water out as it can lose priming with still a few feet of water in the deeper end of the pool. A submersible pump can then be utilized to get all the water out. Make sure the submersible pump fits into the main drain pot.
While draining the pool, washing and scrubbing it down (or sometimes using push brooms) are necessary to thoroughly remove the algae blooms and leaves. When algae and other gunk dries on the surface, it becomes twice as difficult to remove them.
Once the pool is completely clean and emptied, pool acid washing the plaster can commence in the deep end. Do not forget to put on protective clothing and safety equipment especially rubber boots, eye goggles, and an acid-compatible breathing mask.
- Pour the Acid
Proceed by adding equal parts acid or an acid alternative to water in a flower watering can preferably with a long pouring spout. Remember to always add acid to water and never the other way around. A weaker solution (less than a 1:1 ratio) can also be used to avoid damaging the plaster. Pressure washing the pool first before applying acid will significantly reduce the amount of acid necessary.
The pool walls must be moistened before pouring acid over. Pouring the acid mixture on dry surfaces must be avoided. Keep the hose running at all times. A pressure washer is however discouraged from use and a regular garden hose with a nozzle is more preferred to rinse the acid.
The acid should be rinsed completely, otherwise, it will continue to etch the pool plaster. Keep pushing the acid mixture around the pool or spread it continually with water using the hose, a push broom, or an acid brush during this pool acid washing step. Do not let the acid sit too long on the steps as it can wear them thin and rough.
- Neutralize the Acid
After the pool acid washing, the bottom of the pool will be full of foamy, acid puddles. This has to be neutralized before pumping out. Remember to use about 2 lbs. of soda ash for 1 gallon of the acid mixture used. Pool owners can also do a base demand test. A pH test kit can also be used to tell when the water has turned neutral (7.0) or as close to it as possible.
- Pump Out Water Waste
A small submersible pump with a hose can be used to get the remaining acid water out of the pool after pool acid washing. Rinse the bowls of the pool as needed. After the pool has been cleaned thoroughly, it can begin to be filled with water. Remember to reinstall the main drain covers tightly.