How To Fix Hard Water In Fish Tank

Last Updated on July 28, 2021 by

For aquaponics, you do not need to fix hard water in your fish tank because the calcium and magnesium in hard water can be utilized by plants. Hard water naturally occurs from groundwater as minerals from the rocks dissolve into the water. In general, hard water will not harm your fish and can be utilized by plants as micronutrients. Some water treatment facilities add chlorine to ensure prevention of bacterial growth. Although hard water causes calcification in pipes which leads to clogging, there is no immediate harm in hard water. This article will discuss what hard water is and how to make your hard water soft in a fish tank.

Hard water begins from the underground water in your area. Underground rock formations will naturally dissolve in water over time. This increases the concentration of minerals in your water depending on the geological formation in the area. Depending on the area, there will be different concentrations of calcium and magnesium in your water. Hard water will cause precipitation to form in your aquaponics system if your water has a pH above 7. Keeping your water between 6 to 7 pH will prevent clogging and allow the calcium and magnesium to be utilized by the plants.

Hard Water Containing Magnesium and Calcium Can Come In Carbonates, Chlorides, Or Sulfates

Depending on your location, tap water contains different concentrations of dissolved minerals coming from the groundwater source. These minerals come from natural underground rock formations which slowly dissolve into the water. Some treatment facilities undergo chlorine treatment which reacts with the calcium or magnesium forming calcium chloride or magnesium chloride. Calcium and the magnesium come in the form of chlorides, Calcium Chloride (CaCl2), and Magnesium Chloride (MgCl2). Chlorides will damage your bacteria, fish, and plants so dechlorination will be your priority. Otherwise, hard water will contain them as Calcium Carbonate (CaCO3) or Magnesium Carbonate (MgCO3). Another common underground mineral include sulfates which react with calcium and magnesium as well. This will form calcium sulfates (CaSO4) or magnesium sulfates (MgSO4).

Is hard Water Bad For Fish?

Hard water comes in different forms of chloride and sulfates which can harm your fish. According to Kentucky State Water Watch, In less oxygenated waters, sulfates can turn into sulfides (H2S) which is toxic to humans and fish. Plants utilize sulfur in the form of sulfates making it useful for micronutrient requirements of your plants. Keep your water aerated to allow sulfate concentration to be more than sulfides. Chlorides could also harm fish health at low concentrations.

How To Identify What Kind Of Calcium and Magnesium Are In The Water

First, you can check with your State or Local Government Bodies about the groundwater source for your area. This data should be publicly available for your area from the local authorities. Otherwise, the USGS has a general report for the calcium carbonate concentration in underground water supplies across the US. Underground water sources do not change water composition in general unless major land events have happened over the recent years or if you are closer to the ocean or sea.

If you want to ensure the composition of ions in your water; collect a sample and have it tested at your City Public Health Laboratory. Follow these steps to have your water tested:

  1. Collect untreated samples of water from your source in a clean glass container.
  2. Make sure your glass container can hold more than 1 liter or 0.26 gallons of water
  3. Keep in a cool area out of sunlight until sampling
  4. Bring to your local government lab for testing
  5. There are a number of available tests, but for the purpose of finding out what kind of anions are in the water test for:
    1. Sulfates
    2. Carbonates
    3. Chlorine
    4. Calcium
    5. Magnesium
  6. North Dakota State University also provides a complete guide on water testing and understanding the test results from the laboratory.

testing water

Learn more about: How To Remove Calcium Buildup On Fish Tank

How To Soften Hard Water For Fish?

Calcium and magnesium are difficult to remove from water as they do not evaporate, unlike chlorine and sulfur. Using water softener like reverse osmosis filters or using sodium carbonate to trap calcium ions. Both of these processes cost more than it’s benefits. Removing calcium through sodium carbonate will also potentially add sodium in the water which hampers the nutrient uptake of plant roots. Instead, prioritize removing chlorine and carbonates from the water to prepare using hard water in your aquaponics system. Sulfates will not damage your system as well as long as your water is well oxygenated.

Acidic Water Will Prevent Calcium and Magnesium From Forming Precipitates and Allows Your Plants To Take Up The Nutrients

When using hard water for aquaponics, you need to treat your water by dechlorinating, aerating,  and maintaining your pH to be lower than 7 before adding it into the system. Before adding the hard water into the system, dechlorinate your water. As chlorine evaporates into the atmosphere, calcium and magnesium will remain in the water. Use commercial pH down for your water as well. Be sure to use pH down that does not use sodium bisulfate (NaHSO4). Acidic water will prevent the buildup of precipitate from the reaction of calcium or magnesium with carbonates.

After you dechlorinate, aerate, and lower the pH of your hard water, it is safe for use in your aquaponics system. The calcium and magnesium ions as they are micronutrients needed by plants will naturally be used by plant growth in your system. The concentration of calcium and magnesium will decrease as you continue harvesting vegetables and crops from your system.

How to fix hard water in fish tank does not require the removal of calcium or magnesium ions. Rather, improving the condition of plants utilizing these micronutrients without causing problems for your aquaponics system is more beneficial. The simplest solutions to preparing the hard water for use in aquaponics are to dechlorinate, aerate, and lower acidity below 7.  There are different forms and concentrations of water hardness depending on your location. Asking local authorities or having your water tested will give you a clear idea on what the water quality is. Chlorine from water treatment or natural sources could threaten your fish and plant population.

Read more about: How To Clear Fish Tank Water Fast For Aquaponics

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