Water hardness is a measure of mineral particles that have been dissolved into the water, in an aquarium it is generally described in GH (General Hardness) and KH (Carbonate Hardness). Both of these are important when keeping OEBT and shrimp in general.

General Hardness – This mainly a measure of Calcium and Magnesium in the water.

Carbonate Hardness – Is generally referred to the buffering capacity of the water, and is basically a measure of the waters ability to resist change in pH. Unfortunately raising KH often results in raising the PH which means that when keeping aquatic pets that require a neutral pH or acidic water we need to keep the KH relatively low. There are ways to cheat this that will be explained later.

Measurement of Hardness – Probably one of the most confusing parts hardness is how it is measured, hardness is often sited but rarely labeled and depending on the test kit this can be confusing to the new hobbyist so I will try and make it easier to identify what measure is being sited based on the size of the measurement.

  • Degrees of Hardness – Typically measured in  numbers between 1 and 15 (can be up to 30+ for extremely hard water)
  • Parts per Million (PPM or mg/l CaCO3) – Many test strip kits measure both KH and GH in terms of ppm and generally the numbers range between 30-300.

 Conversion –  The conversion between Degrees of Hardness and ppm is 1 degree is 17.9 ppm

Relative Scale

Description                ppm               degrees

Very Soft                 0-53.7            0-3

Soft                         to 89.5           3-5

Slightly Hard            to 160            5-9

Moderately Hard       to 215            9-12

Hard                        to 268            12-15

Very Hard                  268+            15+

Controlling Hardness

To control hardness we must understand what hardness is and how it accumulates. Hardness in water both (GH and KH) will generally increase over time unless you use distilled, reverse osmosis, or rainwater to top off your tank or if your tap water is softer than your desired tank hardness and you do regular water changes. The reason hardness increases over time is because the amount of dissolved minerals stays the same even if the amount of water is reduced through evaporation, so each time you top off your tank with tap water the total mineral content of the tank will increase if there water you use to top off the tank has any hardness at all. Using water that is softer than the tank water will lower the degrees/ppm of the water but the total mineral content is the same, that is why the easiest way to maintain hardness is to only top off the tank with RO water and do water changes with water that is the approximate hardness of the tank water. If you need help figuring out how much water to add to reach a desired hardness then you can use this calculator I wrote http://www.fileden.com/files/2012/3/5/3274377/WaterChangeCalculator.zip

RO/Distilled/Rainwater all have an approximate hardness of 0, there are many guides you can find for rainwater collection if you live in an area where enough rain water falls to reliably use rain water in your tanks, I will not cover how to collect rainwater in this guide but it is the cheapest solution if you live in an area with a decent amount of rain and a low level of pollution, if you live near major highways or industrial pollution collecting rain water may put your shrimp at considerable risk.

Natural Ways to Lower Hardness

Driftwood and some dried leaves (Indian Almond Leaves for instance) can lower overall hardness of water, but keep in mind this is most effective at making hard water less hard, if you are looking significantly lower your hardness large amounts of driftwood/leaves would be required and that will significantly discolor your water (see my product review on Purigen for how to return the water to a lower tint, you can increase the effectiveness of driftwood by making sure a decent water current flows across the surface of the driftwood, this is more difficult with leaves as they tend to follow the current. If you topping of a tank with even moderately hard water do not expect driftwood to have a significant effect on the hardness. Driftwood should be used in conjunction with soft water top-offs/water changes to maintain a lower overall hardness.

Natural Ways to Raise Hardness

Many decorative pieces of rock/shells can raise the hardness over time. Limestone and various sea shells (such as clams) have this effect, and similar to driftwood this is a very slow increase in overall hardness, generally raising hardness is not a problem in the shrimp hobby but this is one way to find a balance of hardness if you are raising a harder water shrimp and your tap water is particularly soft.  Some not so natural ways to raise hardness are sodium carbonate or sodium bicarbonate, and various calcium and magnesium based salts(be sure to check that they are shrimp safe before using anything like this).

Personal Reference

I started my OEBT tank with 90% RO water and 10% aged Austin water (moderately hard about 180ppm) which gave me very soft water. I also added about 1 table spoon of fresh Baking Soda (sodium bicarbonate) to this during the aging of the water to add a bit of buffering capacity. I also keep a ~5lb piece of Mopani driftwood in my tank and a ~2lb piece of Texas Holy Rock (Texas Holey Rock provides necessary minerals in the water by slowly dissolving over time and depositing Calcium, Magnesium, and Carbonate into the water and buffering the water pH) as well as providing save “caves” for the shrimp. I find that the Texas Holey Rock  gives the water and the shrimp the various minerals they need and the driftwood/water changes with R/O water serves to counter the hardness increase of the THR. It works well for me and keeps my PH and hardness fairly stable.