Adjusting water hardness is something that I do not advise you go into lightly. This is a path that will lead to many other questions.

I use RO (Reverse Osmosis) water and it is 0 hardness so I have to reconstitute it to suit my needs. What I do to increase hardness is add 1 teaspoon of Epsom salt, 1 teaspoon of baking soda, and 4 tablets of Natures Bounty 600mg Daily Calcium to my 32 gallon trash can full of RO water.

The Daily Calcium supplement was purchased at Eckerd's Drugstore in the vitamin section. The reason I use Natures Bounty is because they have a minimum of other chemicals within the supplement. Always check what other chemicals are listed on the label besides Calcium or Calcium Carbonate milligrams. This can be misleading.

Well here goes, I am not much of a chemist, but I will try to explain what I understand about water hardness.

Water hardness is the amount of mineral salts that are dissolved in water. Water hardness is made up of two distinct components, General Hardness (GH) and Carbonate Hardness (KH). GH is the measure of Calcium and Magnesium. KH is the measure of Carbonate/Bicarbonate hardness also called Alkalinityor buffering. Most fish prefer 3 to 10 dGH (degree of general hardness) and 2 to 8 dKH.

KH is the buffering ability that allows the water to resist changes in pH when a base or acid is introduced. The higher the degree of KH the more stable your water will remain. This is the component that most people miss in their water. When this level is too low you will see dramatic shifts in your pH range in short periods of time. This problem will also lead to having much trouble with ammonia/ammonium problems. In water with a pH lower than 7.0, the harmless ammonium will be found. If pH rises above 7, the toxic compound ammonia will quickly kill your fish if levels rise too high.

To make a long story short you need to have both hardness levels in sync to keep from having shifts in pH and other related nutrient problems.

Since I am using RO water and not tap water I further supplement my RO water with the following. I add Leaf Zone which is potassium sulfate and iron (plants will love this). This is what is called a Macro nutrient. Next I use Flourish by Seachem. Flourish is what is called a Micro nutrient supplement. It provides a lot of other nutrients and minerals that are found in regular tap water. You may not need to add this to your water. I do because of the use of RO water. Your tap water could be providing some of these nutrients to your tank.

Lastly I also add 1 teaspoon of Kosher salt to 5 gallons of water. This is done for two reasons. First is that I raise guppies and they need the salt, which helps them with parasites. Secondly it helps to increase the overall hardness for my other tetra tanks.

Hope this will help and explain some of the water chemistry question most of us have with soft water situations.