Backyard Aquaponics
A place to discuss aquaponics

By the way, I believe I have read somewhere before that the testing strips aren't that accurate. I am sure someone else could also advise, but it might be a good time to get yourself a master test kit that would do ammonia, nitrite, nitrate, ph and high ph.

Am going to get one of the master test kits soon, am building up a shopping list atm. Have seen professional ones that also have hardness (& calcium hardness). Are these useful in any way for aquaponics? ($139 tho) Havent heard of anyone testing for this so far.

Would also love to test for DO down the track but have only seen testers for up around the $800 mark! must be cheaper options!

We need to be a little careful when discussing "hardness" ... for it's oftened confused and/or confusing...

There are two types of water hardness: general hardness (GH) and carbonate hardness (KH).

A third term commonly used is total hardness which is a combination of GH and KH. This is the test that most "hardness" test kits test for...

Since it is important to know both the GH and KH, the use of total hardness can be misleading and should be avoided.



GENERAL HARDNESS

General hardness is primarily the measure of calcium (Ca++) and magnesium (Mg++) ions in the water.

Other ions can contribute to GH but their effects are usually insignificant and the other ions are difficult to measure...

GH will not directly affect pH although "hard" water is generally alkaline due to some interaction of GH and KH.

GH is commonly expressed in parts per million (ppm) of calcium carbonate (CaCO3), degrees hardness (dH) or, more properly, the molar concentration of CaCO3.

One German degree hardness (dH) is 10 mg of calcium oxide (CaO) per liter.

In the U.S., hardness is usually measured in ppm of CaCO3. A German dH is 17.8 ppm CaCO3. A molar concentration of 1 milliequivalent per liter (mEq/l) = 2.8 dH = 50ppm.

Note that most test kits give the hardness in units of CaCO3; this means the hardness is equivalent to that much CaCO3 in water but does not mean it actually came from CaCO3.

Water hardness follows these guidelines:

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


General hardness is the more important of the two in biological processes.

When a fish or plant is said to prefer "hard" or "soft" water, this is referring to GH. Incorrect GH will affect the transfer of nutrients and waste products through cell membranes and can affect egg fertility, proper functioning of internal organs such as kidneys and growth. Within reason, most fish and plants can successfully adapt to local GH conditions, although breeding may be impaired.



CARBONATE HARDNESS

Carbonate hardness (KH) is the measure of bicarbonate (HCO3-) and carbonate (CO3--) ions in the water, it's "buffering" ability... or "alkalinity".

In freshwater systems with neutral pH, bicarbonate ions predominate and in saltwater aquariums,carbonate ions begin to play a role.

Alkalinity is the measure of the total acid binding capacity (all the anions which can bind with free H+) but is comprised mostly of carbonate hardness in freshwater systems.

Thus, in practical freshwater usage, the terms carbonate hardness, acid binding, acid buffering capacity and alkalinity are used interchangeably.

In an AP system, KH acts as a chemical buffering agent, helping to stabilize pH. KH is generaly referred to in degrees hardness and is expressed in CaCO3 equivalents just like GH.

In simple terms, pH is determined by the negative log of the concentration of free hydrogen ions (H+) in the water.

If you add a strong acid such as nitric acid to water, it completely dissociates into hydrogen ions (H+) and its "conjugate base" or "salt", NO3- or nitrate.

The hydrogen ions freed in the reaction then increase the concentration of hydrogen ions and reduce the pH. Since nitric acid is the end product of the nitrogen cycle, this explains why AP system pH tends to decrease and nitrates tend to increase over time.

When an AP system has some carbonate buffering in it, the bicarbonate ions will combine with the excess hydrogen ions to form carbonic acid (H2CO3) which then slowly breaks down into CO2 and water.

Since the excess hydrogen ions are used in the reaction, the pH does not change very much. Over time, as the carbonate ions are used up, the buffering capacity will drop and larger pH changes will be noted.

From this it is clear why AP systems with low KH seem unstable, and can drop rapidly to pH 6.0 - as acid is produced by biological action, the KH is used up; when it is gone, the pH is free to drop rapidly as H+ ions are generated.

Still unsure about the diff between pH and high pH tho.