Mixing Saltwater

Saltwater is going to be mixed many times from the very creation of the aquarium way into the future. It is my opinion that a lot of people make this into something which takes more time than it actually needs to be.

All you need to do is spend a bit more time when performing the first water change to make it a lot easier in the future.

Both John and myself recommend the use of reverse osmosis water be this purchased from the local fish shop or created in the aquarists own home therefore when purchasing the salt mix it is imperative that one be purchased which has been specifically manufactured to be used with reverse osmosis water.

The net gallonage of the aquarium should be known from when the aquarium was initially filled with water therefore it is relatively simple to work out how much water will need to be removed from the aquarium for a 10% water change to be performed. In this example we will pretend that the net gallonage of the aquarium is 100 gallons therefore a 10% water change would be 10 gallons. This figure should be noted down for future use.

It should be remembered that fresh newly created reverse osmosis water should be used and it should be heated up to the same temperature of the display aquarium prior to adding any salt.

Having purchased the sea salt it is fairly straight forward to ‘guess’ the amount required to meet the intended specific gravity of the aquarium by looking at the suggestions/recommendations of the manufacturer.

When measuring it is recommended that you actually measure slightly less than you believe you require. Once you have measured the salt do not add it to the water weigh it first and make a note of the reading.

Add the salt to the water and give it a really good stir using a device such as a clean wooden spoon to initially mix it in. Add either an air pump or a small powerhead and leave it alone for 8-12 hours. This will allow the salt to fully mix into the water.

After this time measure the specific gravity with a hydrometer or other measuring device such as a refractometer.

At this point you will have one of three scenarios:

  1. The specific gravity reading is to low. Measure out a little more salt and make a note of the weight. Add this salt to the mixing device and allow more time for the salt to mix and then test the specific gravity again. If more salt is needed then proceed as before ensuring that any new salt measured it weighed and recorded. Once the specific gravity reading is correct then simply add all the salt weights together for future use and record this information.
  2. The spcific gravity reading is to high. Add some more reverse osmosis water to the mix noting the amount added for future use. Give the water time to warm up and then test again. If the reading is still to high then add some more water and record how much was added. Once the reading is correct then add the amount of water together and record this information.
  3. The specific gravity reading is correct.

Taking your time on your first water change will allow you to identify how much salt you need to add to the required amount of water. When new water changes are to be performed you can create the correct amount of reverse osmosis water and weigh out exactly the correct amount of salt required.

It needs to be noted that using this method although does save you considerable time when mixing saltwater does not mean that you should not test the specific gravity each time. It is recommended that you continue to test each and every time you create new salt water and always ensure that you keep your measuring device clean.


Mixing Saltwater
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  1. Again, Please use a refractometer! As hydrometers are extremely inaccurate, they usually read .002-.005 low. That mean the salinity on a hydrometer may show 1.025, but you are actually 1.030! Hydrometers do not auto compensate for differences in temperature as most refractometers do.

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