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Bicarbonates & Limescale

High bicarbonates (HCO3) are anions (negatively charged ions) found in many of our freshwater sources in South Carolina, especially in deep water wells. In the presence of calcium (Ca2+) or magnesium (Mg2+), bicarbonates can turn into deposits commonly termed “scale” or “limescale”. The deposits typically appear as white “stains”, that become flaky as they build up (hence the term “scale”). Sometimes the scale can take on a crumbly appearance and be a light tan or brown in color.

How Solids Form

When calcium (Ca2+) or magnesium (Mg2+) are present in the water with bicarbonate, they combine to create the soluble compounds calcium bicarbonate Ca(HCO3)2 or magnesium carbonate Mg(HCO3)2, respectively. As the water dries, these soluble compounds form the solids calcium carbonate (CaCO3) and magnesium carbonate (MgCO3). In a similar fashion, when Ca2+ and Mg2+ are present in the soil, and bicarbonate in the soil water, they too will bond and form the same solids mentioned previously.

Scale deposits can be found on plant leaves and sides of pots.

Scale deposits can be found on plant leaves and sides of pots.
Dara M Park, ©2018 Clemson Extension

Why Bicarbonates are so Bothersome

Consider the effects of scale on irrigation systems and soil porosity. Lime deposits can build up and clog pipes and emitters (including sprinkler heads, drip lines, or microspray heads). These residues also clog soil pores. Scale deposits can be found on plant leaves and sides of pots. They are typically not seen on turfgrasses because the leaf blades are removed so often that the scale does not have time to build up.

Calcium and magnesium assist in aggregating soil by providing a good soil structure, with a balance of macropores for air movement and drainage, and micropores for water retention. The removal of calcium and magnesium from the soil surfaces means there is less aggregation of soil particles. This results in more individual soil particles that when dry, shift close together, filling in macropores (and some larger micropores too) and resulting in less air movement and drainage within the soil. The soil particles compact easily, and can form a paper-thin crust layer of soil on the surface. The crust does not allow water and air to move into the soil. Sandy soils are least likely to develop a crust, while clays are most likely to develop a crust.

Bicarbonates increase the soil’s pH, making some nutrients less plant available. In addition, bicarbonate can displace the uptake of other nutrients, resulting in bicarbonate root toxicity and plants becoming chlorotic.

Since scale can form on anything high-bicarbonate water comes in contact with, issues can develop with plumbing inside the home as well. It is most evident on shower heads, sink faucets, and other places where hot water is commonly used. The warm pipes and surfaces cause quick evaporation of water when turned off, resulting in a faster buildup of the scale. If not taken care of, clogging will decrease water flow.

Managing Scale Deposits

First, sample the water. A water sample can be sent to the Clemson Agricultural Service Laboratory by taking them to a local Clemson Extension Office. Once the results are received, look at the pH and bicarbonate levels. If the pH is above 7.4, high amounts of bicarbonates are likely present. If the bicarbonates are greater than 1.5 meq L-1 or (90 mg L-1), there is a potential issue.

For irrigation water, the main way to manage high bicarbonates is to add an acid. For small lawns and home gardens, the most common method is broadcasting sulfur along with using acid forming fertilizers such as urea based nitrogen fertilizer. For larger landscapes, an in-line injection system with a back flow preventer can be installed to inject an acid. Regardless of which approach is utilized, frequent applications at low rates gives the best results. Consult your county extension agent for more information. If a thin surface crust is noticed, break it up using a rake, cleats, or pitch fork. For larger landscapes, use a hollow or solid tine drill for aerification.

For the home, a common practice for reducing the effects of limescale is to install a water softener. To clean affected shower heads or faucets, fill a large sandwich bag with white vinegar and submerge your shower head or faucet in the vinegar. After allowing it to sit for a few hours, remove from the bag, and clean and dry it. If the flow is still low, disassemble the units and soak any scaled pieces in vinegar. Towel drying shower heads and faucets after each use will also reduce the build-up.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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