Wine Country Pools & Supplies is not responsible for any damage caused from the use of this guide.
This article is meant to help anyone with a pool or spa that wants to better understand water pH and water Alkalinity levels. Always follow the instructions of any chemical before adding it to your water. If you are unsure, seek professional help with your water chemistry. Using the incorrect chemical or amount of chemicals can damage equipment and create health problems for anyone using the pool or spa.
Is my water acidic and what can I do?
An acceptable pH range is between 7.2 and 7.8. Anything below 7.2 is considered to be potentially corrosive and anything above 7.8 is scale forming.
The ideal pH range is between 7.4 and 7.6. On a side note, chlorine is more effective when the pH is lower since it has more H to bond to and become HClO. Chorine would prefer the pH to be closer to 6.0 for maximum efficiency; only at that level the water etch the plaster, corrode the equipment, cause skin and eye irritation, and other various (and expensive) problems. However tempting it might be to lower the pH to kill possible water containments, avoid lowering the water pH below 7.4.
Almost all liquid test kits can be used to test pH and most strip testers. If you are using a liquid tester and the pH only shows a yellow color (whereas orange, pink and purple are the only choices on 90% of liquid test kits, see picture of typical test kit above), the pH level has fallen far below the given scale and is in the extreme corrosive stage.
Because the pH scale is logarithmic, the closer the scale is to each extreme end (zero on the low end and 12+ on the high end), the more solution is required to move back one full digit (it takes 10 times more acid to move the scale from nine to eight than it would to take the scale from eight to seven).
Raising and lowering pH:
To lower pH, you want to add H’s (hydrogen) to the water. The easiest way to do this is with liquid Acid, also known as Muriatic Acid. This has a natural pH of less than 0.5, which is why it is added slowly. Adding too much acid can be a costly mistake.
Always add less than you think it needs, then add more later if necessary. Give the acid time to circulate before retesting. Allow it anything from a few hours to a full day.
Storing liquid acid can be dangerous. The plastic bottles they come in will eventually harden and crack over time. It is also easy to spill a loosely capped bottle or puncture the side. The acid is dangerous to kids and/or any pets that might come in contact with the bottle. An alternative to liquid acid is dry acid, known more commonly as “pH down.” While more expensive and less effective (has a pH between 1.0 -2.0), it is generally safe in its powdered form.
To raise the pH, the most common chemicals are soda ash (also called “pH up,” which has a pH of around 12+) or Alkalinity up.
Note: do not use household baking soda. The difference between baking soda and soda ash is that soda ash has been tested under various conditions and comes with written instructions for the amounts required to add to a pool/spa water.
Use the recommend amount of soda ash. The worst that can happen of using too much (causing a high pH) is that it will cloud the water and cause scaling over time, usually around the water line.
If the pH reading is so low that it’s off the scale (i.e. yellow), it can take multiple pounds of soda ash to bring the levels back up to the 7.4 range. In extreme cases, the water will change colors when soda ash is added (usually a dark milky blue).
If this happens, add soda ash and then wait a few hours before retesting, allowing the system to filter the whole time. Check the filter every few hours; it may have a blue or purple scale on it that was filtered out from the water.
Clean the filter to allow for proper filtration until the water is clear. This process can take 24 hours or longer.
Alkalinity friend or foe:
At its best, Alkalinity is not currently hurting your pool/spa chemistry. At its worst, it is casing the pH to change seemingly at random, or not at all after adding additional chemicals.
Total Alkalinity is defined as all of the dissolved alkaline materials currently in a water sample. A Total Alkalinity value describes water’s resistance to a change in pH.
If the Total Alkalinity is too high (over 120 parts per million), any acid added will have a small effect.
If the Total Alkalinity is too low (under 40 parts per million), any acid added will have great effect.
The ideal range is between 80-120ppm (parts per million).
In general, alkalinity changes very slowly on its own. If it does get out of range, the pH levels will either jump from low to high or not change at all after adding chemicals. If either of these happens, perform a total alkalinity test.
When testing alkalinity with a liquid test kit, there are usually 3 bottles involved. Not all test kits can test alkalinity and not all test strips test for alkalinity.
Alkalinity and pH are directly related. Low alkalinity can cause similar problems to low pH and high alkalinity can cause similar problems to high pH. You will raise and lower alkalinity in the same manner as you would raise and lower pH. This also means that changing either pH or alkalinity will affect the other. Always get the alkalinity into an ideal range first; then work on the pH since a balanced alkalinity will cause a stable pH change.