Calcium-To-Magnesium Ratio Calculator For Shrimp Keepers

Introduction

Ensuring the right balance of minerals in your tank water is critical to successful shrimp keeping. The wrong amount leads to molting problems, poor offspring survival, and worse immune function. Negative effects can also be seen in aquatic plants, leading to serious problems with a tank ecosystem. There are two ways to ensure the right mineral content in your water.

#1 - Use a Remineralizer With Pure Water

The most reliable way to achieve the right amount and ratio of key minerals is to use water that has been purified via reverse osmosis filtration or distillation (RO/DI water), then adding minerals in using a shrimp-specific remineralizer. While there are many different ones available that work well, we recommend the Salty Shrimp brand due to our experiences and the wide availability of their products.

#2 - Check and Adjust Tap Water Levels

If you use tap water instead of remineralized water, then it’s tough to know whether the right ratio of minerals are present, specifically calcium (Ca) and magnesium (Mg). You may have General Hardness in a healthy range but still experience molting problems (Click here for background information on GH in shrimp tanks). GH is one useful test that tells you if the right sum of calcium and magnesium are present, but GH does not tell you whether they are present in the right ratio. Your GH could be made up of 100% calcium and 0% magnesium, or the opposite, neither of which are healthy. The recommended Ca:Mg ratio is roughly 2-5 parts calcium for every 1 part magnesium by weight. This is shown by environmental data from streams where Neocaridina live naturally (5:1 Ca:Mg) and from testing the Salty Shrimp remineralizers (2:1 Ca:Mg). The remineralizer is used by a wide range of shrimp keepers and has been shown to work consistently well, so we generally recommend aiming closer to that ratio, as opposed to the 5:1 seen in streams in Taiwan, where molting success frequency has not been tested.

Tap water in the US has around a 3:1 ratio and the right total GH on average, so many shrimp keepers have success using tap water to raise relatively insensitive species like neocaridina (cherry shrimp), ghost shrimp, vampire shrimp, bamboo shrimp, and amano shrimp. That being said, if you don't test your water then you are taking a risk. The only way to find out if your tap water actually supports the shrimp you want to keep is to either:

• Check if your County Water Quality Report provides calcium and magnesium levels (search "[county name] water quality report in Google")
• Put shrimp into an established tank and see if they have molting problems or not
• Test your water to determine GH and Ca:Mg ratio, then adjust accordingly

If you experience molting problems or want to test your water before adding shrimp to be careful, then the following procedure explains how to do so. The rest of this article explains the most cost-effective way to test your tank's calcium and magnesium levels, then how to calculate the Ca:Mg ratio. If the ratio is far off of the recommended 2:1 ratio, then we also explain how to fix it by adding the missing minerals.

Instructions:

(Credit for modified API Calcium Test Kit procedure in freshwater goes to Planted Tank forum user Immortal1)

1. Place 10mL of your tank water into the container. (Double volume for 5 mg/L accuracy)
2. Add 20 drops of API Calcium Test Kit Bottle 1 to the container. (Double drop amount for 5 mg/L accuracy)
   
3. Shake the container for 10 seconds.
4. Shake Bottle 2 vigorously for 10 seconds.
5. Add drops from Bottle 2 to the container until you see a change from pink to blue (keep going if purple). Be sure to count the number of drops added and shake well between drops.
6. Multiply the number of drops by 10 to get the calcium concentration in mg/L or ppm. Multiply number of drops by 5 if Step 1 and 2 were doubled.
   
   • Example: 4 drops * 10 = 40 mg/L calcium

Step 2: Determining General Hardness (GH) of Freshwater Tanks

Follow the instructions of the API GH Test Kit (or whichever liquid GH test you prefer – do not use strips) to determine the GH of your tank.

Step 3: Determining Magnesium Concentration and Current Ca:Mg Ratio

Enter in your GH (select units) and calcium concentration from Step 1 to automatically calculate magnesium concentration and Ca:Mg ratio.