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Ok, I keep seeing postings everywhere asking questions about pH, hardness, softness and the like. I hope this helps, if not, at least I tried.

Water Chemistry
Most aquarists know that pH is the measure we use for water hardness, however pH is actually only a measure of hydrogen (H+) ions in the water we are testing. In fact pH in latin stands for the power of hydrogen.
If there is a high hydrogen (H+) concentration in the water then the water is said to be acidic (having a pH below 7.0). If the water is low in hydrogen content (above 7.0 pH) then the water is considered alkaline. Decaying plant matter, organic wastes, uneaten foods, will all cause hydrogen to form in the water thus possibly causing it to become more acidic.
A neutral pH is measured at 7.0. For planted aquariums a pH of between 6.7 and 7.0 is to be desired, however there are several species of plants which prefer either higher or lower pH levels to thrive.
One side benefit to acidic water is the higher concentration of hydrogen causes ammonia to form as the less toxic ionic ammonium (NH4+), while in a higher pH, that above 7.0, due to the lowered amounts of hydrogen the more toxic non-ionic ammonium (NH3) forms.
Now, if all that isn’t confusing enough, lets look at dKH and dH. dKh is the measure of carbonate hardness, which is the measure of concentrated carbonates and bicarbonates in the water. If the dKH is too low you can add tap water (which has carbonate hardness). If you still need to raise the dKH (rift lake cichlids for example), you can add common baking soda.
dH refers to water hardness, which is the concentration of calcium ions (Ca+) and magnesium ions (Mg+) in the water. A high dH reading means that the water is hard, while a low reading means the water is soft.
Usually dKH values are to high instead of to low. If the dKH is to high and you need to lower it you can add distilled water or purified water as from reverse osmosis and deionization.
Another way to lower the waters dKH levels would be with the use of peat moss. Peat moss binds with Ca+ and Mg+ and in the process releases tannic acid and gallic acid. These acids increase the acidity of the water, which in turn causes some bicarbonates to be converted to CO2, (carbon dioxide), which in turn lowers dKH. The drawback to peat is that it is slow acting and will tint your water a slightly yellowish color. The coloring can be removed by placing activated carbon in your mechanical filtration unit.
Water can also be softened with synthetic resins. You can use a sodium based resin, or a deionizing resin. A sodium based resin is like that used in home water softeners. Chemically, this means of softening is not ideal for the aquarium as it doesn’t remove all the cations in the water, such as salt, which contribute to the waters hardness. Deionization resins are far better than the sodium based resins. Deionization resins use 2 resins, cationic resin in hydrogen form, and anionic resin in hydroxyl form. Cationic resins replace the positively charged ions in the water such as Ca+ and Mg+ with hydrogen ions. The anionic resin replaces chloride, bicarbonates, and carbonates with negatively charged OH-.
A side effect of the deionizing resin is that the resulting H+ and OH- combine to become H2O, (water). Water purified this way eliminates both Ca+ and Mg+ hardness (dH) and carbonate hardness (dKH). The downside, these resins can only be recharged with a strong acid or replaced.
The carbonate hardness (dKH), acidity (pH), and the amount of carbon dioxide (CO2) in the water all work together to determine the overall quality of the water, with each affecting the other to some extent.
The pH of your tank is determined by the levels of both CO2 and dKH. The CO2 generates carbonic acid, lowering the pH. The dKH acts as a buffer to stabilize the pH.
Decorations in your tank can affect the pH, dH, and dKH of your water. Crushed coral for example may cause your pH,dH, and dKH levels to rise.

Great post, Tanker! I copied it to a document and I am saving it, hope you don't mind.

__________
"To steal ideas from one person is plagiarism; to steal from many is research."
researched from Steven Wright

Don't mind at all, just glad someone actually read it.

Someone else read it. Very good article indeed! Thanks.

WOW, You cleared up some major questions!! Great article!!

thankyou so much. ive been having problems with the hardness and this should help a lot.