What is water hardness? 

Water hardness is, at its most basic, the presence of certain minerals in water. Historically, water hardness was a measure of water’s ability to form lather during laundering. Harder water, due to it’s high calcium/magnesium content, would not lather as readily (or at all). For a long time there were many different scales for this, due to different countries with different languages measuring different chemical reactions.

Today we measure Total Hardness, the total amount of both calcium and magnesium in the water, in parts per million (ppm). There are also individual tests for magnesium hardness and calcium hardness. Total hardness is not useful for float tanks, since we add about 300,000ppm of magnesium sulfate to our water.

The measurement you would potentially find useful to your tank would be calcium hardness, and even that is not really necessary to monitor.

Why do we (usually) measure water hardness?

High calcium hardness can cause scaling, a crusty precipitation of excess calcium. This is especially harmful to water heaters, as calcium has an inverse temperature solubility; in water, calcium is exothermic, which means it gives off heat when combining with water. This also means that the warmer the water, the less calcium can remained dissolved in it. For this reason water heaters are particularly vulnerable to excessive scaling, which can cause the heater to work harder to less effect. This not only raises the cost of heating your water, but will ultimately result in the heater failing.

Water with low calcium hardness will draw calcium out of any nearby sources, causing significant pitting (the formation of tiny craters) on calcium rich surfaces such as grout, plaster, and concrete. This is not something you are likely to experience in a float center, however, as anything that might be affected by pitting would have already been destroyed by salt. If you do see pitting, it means your room is not water-tight, and you’ve got much bigger problems than just your water hardness.

The best time to measure hardness in your water is before you put it in the tank. Local water sources vary widely, so testing the water directly from the source will give you the best idea of what, if any, corrections need to be made. Ideally, water going into your tank will register between about 100-250ppm.

What do I do about water hardness?

Any problems you might encounter with hardness are almost entirely determined by the tap water in your area, and the solutions for hardness issues should be implemented before the water even reaches the tank. Issues with water hardness are not going to be a major issue in your tank, but will definitely affect things like water heaters, or electronic/mechanical machinery the water passes through.

In the case of high calcium hardness in your water supply, there are numerous commercially available water softeners. If the water in your tank is already too hard you can attenuate water hardness by adding soft water when you periodically top off your tank.

The good news is that the best way to prevent calcium scaling is with magnesium. In one of the few instances where all this salt is not just destroying everything you hold dear, magnesium disrupts calcium precipitation by mixing with the calcium, softening it, and discouraging further precipitation.

For low calcium hardness in tap water simply adding calcium will solve the problem. The most common way to raise your hardness in the pool industry is calcium chloride.

Resources
General information about water hardness, the benefits of soft water, and water treatment options
http://www.hardwater.org/

A few posts that include in depth information on water hardness and it’s history
http://www.thekrib.com/Plants/CO2/hard-slu.html

Information on calcium hardness from Taylor Tech’s official website
https://www.taylortechnologies.com/ChemistryTopicsCM.ASP?ContentID=70

BASIN (Boulder Area Sustainability Information Network) on water hardness
http://bcn.boulder.co.us/basin/data/NEW/info/Hard.html

Short articles with pictures and information on calcification
http://www.water.ncsu.edu/watershedss/info/hardness.html

Very helpful article, includes visuals of how magnesium disrupts calcification
http://reefkeeping.com/issues/2006-06/rhf/