Water Hardness – The Problem:
The “hardness” of water is determined by measuring bicarbonate levels; the harder the water, the higher the percentage of calcium carbonate and magnesium carbonate content usually found in solution. When phosphoric acid is added to lower pH, the bicarbonates are burned off as carbon dioxide and water, but the calcium and magnesium ions react with the phosphorous to produce the acid salts calcium phosphate and magnesium phosphate. Calcium and magnesium phosphate are about 95% water insoluble, so most of the salts precipitate out of solution. The calcium and magnesium precipitates become unavailable to the plant, and over time they form lime scale deposits that clog pumps, irrigation lines and emitters.
Water Hardness in the UK
Most of the UK has “hard” water – water with a high mineral count, this can be seen in the map to the right.
The Commercial Solution
Commercially, the best solution for hard water problems is to use nitric acid to lower pH. Nitric acid reacts with calcium and magnesium to form calcium nitrate and magnesium nitrate, which are about 98% water soluble. The calcium and magnesium ions remain available to the plant, and little precipitate is formed. Unfortunately, nitric acid is a very aggressive chemical and is dangerous to handle, which makes it impractical for hobbyists and objectionable for many commercial growers, as well. Special ventilation and handling equipment is required, and even a minor accident can cause serious burns.
Another problem with hard water is high pH and buffering capacity. It is often necessary to use many times the amount of phosphoric acid to lower the pH of well water as compared with city water, sometimes resulting in a phosphorous toxicity. Although phosphorous toxicity has no direct symptoms, it causes zinc deficiency, iron deficiency and magnesium deficiency as toxicity increases. To prevent phosphorous toxicity, a reasonable compromise is to use a combination of phosphoric and nitric acids, sometimes called “phostric acid”, to lower pH. But if the customer has to mix his own acids, the handling problem becomes an issue once again.
Some hobbyists try to solve hard water problems by using a water softener. This is a poor choice since most water softeners simply exchange calcium and magnesium ions for sodium ions. Sodium is not an essential element for most plants and can become toxic to plants over time as it accumulates in the plant tissue.
Another option for hobbyists is to use reverse osmosis water. Reverse osmosis removes all of the calcium and magnesium carbonates from the raw water, but it also reduces the water’s buffering capacity. Wild fluctuations in pH are often seen as the plants go through various growth stages, normally rising during high nitrate demand and lowering during high potassium demand. A better choice is to use a 50/50 blend of RO water and tap water. The tap water adds back a little buffering capacity to the solution and helps stabilize the pH over time. The down side is that RO filters are relatively expensive to purchase and maintain, and a lot of water is wasted in the filtering process.
The Indoor Hobby Gardener Solution:
The best solution for hard water problems is to use a hard water nutrient formula along with an amino acid chelator. The hard water nutrient formula adjusts for the extra minerals in the hard water, and the amino acids keep the minerals soluble and available to the plant.
Amino acids such as glutamic acid, aspartic acid and glycine are intermediate chelators. They attach to the calcium and magnesium ions in hard water, preventing them from reacting with phosphoric acid, thus eliminating the precipitation of insoluble salts. No lime scale is formed. Instead, the calcium and magnesium ions are easily transported into the plant and released where they are needed.
Amino acids also act as biostimulants. For example, glutamic acid stimulates root cells to open calcium ion channels. Calcium is imported into the plant thousands of times faster than through simple diffusion. Calcium not only remains available to the plant, it is taken up by the plant much more efficiently. Since the calcium and magnesium salts of pectic acid, together called “pectin”, is the substance that glues the cell walls together, the plant is greatly strengthened.Water and minerals are taken up more efficiently and the plant cells are protected against pathogen and temperature stress.