General Hardness (GH)
General hardness (GH) refers to the dissolved concentration of magnesium and calcium ions. When it is said that some plants prefer ``soft'' or ``hard'' water, it is (GH) (not KH) that is being referred to.
It Should Be Note: That (GH), (KH) and (pH) Although as different as they are all three properties are distinct, they all interact with each other to varying degrees, making it difficult to adjust one without impacting the other. That is just one reasons why that BigToke recommends that beginner hydro-newbie’s are advised NOT to tamper with these parameters unless absolutely necessary, or under the direct supervision of a mentor or a very experienced grower who understands the basic properties of water chemistry. As an example, ``hard'' water frequently often comes from limestone aquifers. Limestone contains calcium carbonate, which when dissolved in water increases both the (GH) (from calcium) and (KH) (from carbonate) components. Increasing the (KH) component also usually increases pH as well. Conceptually, the (KH) acts as a ``sponge'' absorbing the acid present in the water, raising the water's (pH).
Water hardness follows the following guidelines. The unit (dH) means ``degree hardness'', while (ppm) means ``parts per million'', which is roughly equivalent to mg/L in water. 1 unit dH equals 17.8 ppm.
0 - 4 dH, 0 - 70 ppm : very soft
4 - 8 dH, 70 - 140 ppm : soft
8 - 12 dH, 140 - 210 ppm : medium hard
12 - 18 dH, 210 - 320 ppm : fairly hard
18 - 30 dH, 320 - 530 ppm : hard
higher : liquid rock (Lake Malawi and Los Angeles, CA)
Did you folks know that by measuring the salinity of your hydroponics systems you can get the total amount of dissolved substances. Salinity measurements count both (GH) and (KH) components as well as such other substances as sodium. Salinity is usually expressed in terms of its specific gravity, the ratio of a solution's weight to weight of an equal volume. One component of salinity that neither GH or KH includes is sodium. Is knowing your Bio-Systems water's salinity very important in nutrient management and long term use? Is knowing (pH), (GH) and (KH) suffices important to any hydro-grower? I will discuss this at a latter time but for now I made up something for you, this is a basic 3D representation of what I am trying to say, once you understand the makeup of basic water chemistry you will have a better understanding of what’s happening in your system.
Nutrients and Trace Elements
In addition to (GH), (KH), (pH) and salinity, there are a few other substances you may want to know about. Most tap water contains an assortment of nutrients and trace elements in very low concentrations. The presence (or absence) of trace elements can be important in some situations, specifically: [list][*]nitrates, which are in direct conjunction with the NITROGEN CYCLE
[*]phosphates, the second most prominent nutrient. Phosphates have been linked to algae growth. If you have persistent algae problems, high phosphates may be a contributing factor, let me say something here, I do not believe that the lucas formula for the Bio-Buckets use it at your own risk. To control algae, only if not using the Bio-Bucket System, frequent partial water changes are often recommended to reduce nutrient levels. If growing in a Bio-Bucket System that I have laid out, there will be no problems for you because the Beneficial Bacterium will control all algae.
Altering Your Water's Chemistry
Hardening Your Water (Raising GH and/or KH)
The following measurements are approximate; Note that if your water is extremely soft to begin with (1 degree KH or less), you may get a drastic change in pH as the buffer is added.
To raise both (GH) and (KH) simultaneously, add calcium carbonate (CaCO3). 1/2 teaspoon per 100 liters of water will increase both the (KH) and (GH) by about 1-2 (dH) degrees of hardness
Did you know….the (KH) calcium carbonate
and the (dH) degrees of hardness
thereof, are the determining factors of your waters buffering capability’s, in other words let’s say that your (pH) to high, and you have to add LOT’S
of ph-up to get it back to normal, that would tell me that your waters degrees of hardness
which is calcium carbonate
is very low!! But if you only had to add a little amount of ph-up that would mean that you (KH) plus (dH) are not to bad off……whoops I hear another one of those little bells going off!!!
To raise the (KH) without raising the (GH), add sodium bicarbonate (NaHCO3), commonly known as baking soda. 1/2 teaspoon per 100 Liters raises the (KH) by about 1 (dH). Sodium bicarbonate drives the pH towards an equilibrium value of 8.2.
Raising and Lowering pH
One can raise or lower (pH) by adding chemicals. Because of buffering, however, the process is difficult to get right. Increasing or decreasing the pH (in a stable way) actually involves changing the (KH). The most common approach is to add a buffer whose equilibrium holds the pH at the desired value. This was what I was talking about of the Bio-Buckets earlier when I said: that if a hydro-system that did not build upon it’s self, then it could not sustain life. Did you know….I’ll bet you didn’t know that the Bio-Bucket System is built around these four basic principals and the support thereof, and that is the (GH), (KH), (pH) and (Salinity).
Note that the exact amount of quantity needed for (pH) up or down depends on the water's buffering capacity. In effect, you add enough acid to use up all the buffering capacity. Once this has been done, decreasing the (pH) is easy. However, it should be noted that the resultant (lower-pH) water has much less (KH) buffering than it did before, making it more susceptible to (pH) swings when (for instance) nitrate levels rise. Warning: It goes without saying that acids are VERY
dangerous! Do not use this approach unless you know what you are doing, and you should treat the water BEFORE
adding it to your hydro-system, this is just another reason that I recommend tap-water if possible.
Products such as ``pH-Down'' are often based on a phosphoric acid buffer. Phosphoric acid tends to keep the (pH) at roughly 6.5, depending on how much you use. Unfortunately, use of phosphoric acid has the BIG
side effect of raising the phosphate level in your hydro-system, stimulating algae growth. It is difficult to control algae growth in a hydro-system with elevated phosphate levels.
Did you know…..that one safe way to lower (pH) WITHOUT
adjusting (KH) is to bubble CO2 (carbon dioxide) through your hydro-system. The CO2 dissolves in water, and some of it forms carbonic acid. The formation of acid lowers the (pH). Of course, in order for this approach to be practical, a steady source of CO2 bubbles is needed to hold the (pH) in place. As soon as the CO2 is gone, the (pH) bounces back to its previous value. The high cost of a CO2 injection system makes it non practical for hydro use as a (pH) lowering technique. (for inexpensive do-it-yourself alternatives). CO2 injection systems can be found almost every were on the internet because the additional CO2 stimulates plant growth.
Softening Your Water (lowering GH)
"Soft water" is a relative term, but water to be soft must contain low amounts of dissolved calcium and magnesium, which cause water to be hard.
Milligrams per Liter Grains per Gallon
Soft 0 to 60 mg/l 0 to 3.5 gpg
Moderate 61 to 120 mg/l 3.5 to 7 gpg
Hard 121 to 180 mg/l 7 to 10.5 gpg
Very Hard over 180 mg/l over 10.5 gpg
Usually the best home water softeners soften water using a technique known as ``ion exchange''. Your may see this as RO/DI That is, they remove calcium and magnesium ions by replacing them with sodium ions. Although this does technically make water softer, and your plants can tell noticeable difference. That is, plants that prefer soft water don't like sodium either.
Hard water can also be softened by diluting it with distilled water or R/O water. R/O (reverse-osmosis) water is purified water made by a R/O unit. Unfortunately, R/O units are too expensive ($100-$500) for most hobbyists, but distilled water can also be almost purchased at any stores, but for most folks the expense and hassle are not worth it.