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Salt is mixed with clean freshwater to produce saltwater. It is a good idea to buy more salt than you need initially, since you will need to mix new saltwater for water changes. Just make sure you keep it in a dry, cool place.

There are many options for salt: all are good and offer different parameters, promises and cost. I use Instant Ocean Reef Crystals in my other tanks, which is a good quality, reasonably priced option and, since I have a lot of it in hand, will use it for this tank. I buy the 200 gallon box, but we can get away with less for this tank. If you buy the 160 gallon option, you get a nice bucket as a bonus! It often goes on sale on Amazon, so keep an eye out for that.

Mixing Saltwater

The procedure for mixing saltwater can vary depending on the manufacturer's instructions, so pay attention to them. For Instant Ocean Reef Crystals, here are the instructions:

1) Mix Reef Crystals® with ordinary dechlorinated tap or purified water. NOTE: To prepare small quantities, use 1/2 cup of Reef Crystals per each U.S. gallon of water. Mix as directed.

2) Stir vigorously to ensure a good mix. Although the Reef Crystals solution may be used immediately, we suggest aerating the water until it achieves oxygen/carbon dioxide equilibrium.

3) Measure specific gravity with an Instant Ocean® Hydrometer.

Recommended Specific Gravity Range: 1.020-1.026 at 77°F.

NOTE: 1.4 lbs of Reef Crystals is formulated to create 5 gallons of saltwater at a specific gravity of 1.021.

4) Adjust salt level accordingly. If specific gravity is too low, add more Reef Crystals. lf too high, add more dechlorinated water.

5) Change 20% of aquarium water every two weeks to maintain optimum water quality.

There's a lot to unpack there.

  • For starters, we will not be using "ordinary dechlorinated tap" water. As we discussed, we will be using zero TDS RO/DI water.

  • We're going to follow their recommendation of 1/2 cup per gallon and see where we end up.

  • We have no way of knowing when the water has reached "oxygen/carbon dioxide equilibrium", so we're going to do our best in that regard.

  • We won't be using an "Instant Ocean® Hydrometer" since they are woefully inacurate. We'll talk about measuring the salinity in the next article.

  • Their note about using 1.4 lbs to achieve 1.021 specific gravity is mostly useless since that is not a specific gravity that we ever want in our tanks.

  • Their advice about water changes feels a bit misplaced here.

In general, you get the water ready, add salt slowly and mix it up until the water is clear. In some cases, you have to heat the water to prevent precipitation, but that is not the case with this salt.

Get the Water Ready

We're going to mix about 30 gallons of saltwater, so we need a container large enough to hold it. Since I have more than one tank, I use a Rubbermaid Brute 44 gallon trash can with a lid which can be purchased for about $45. I also bought a dolly for it, which is an invaluable help in moving the trash can around, even when it is full of water.

Although there are many cheaper alternatives, most of them are not strong enough to hold as much water as the capacity they advertise. So be careful and, if in doubt, get a Brute.

Once the trash can is clean and in position, we can start filling it up with clean fresh water which begs the question: how do we know when we have 30 gallons?

This is what I do:

  • Get a container that holds exactly one gallon of liquid. This can be a bucket with gallon marks, or a one gallon milk jug.

  • Start a timer and then fill it with RO/DI water stopping the timer when it is full.

  • Write down how many minutes that takes.

  • Multiply it by 30 and write it down.

In my case, it takes my RO/DI system about 3 minutes to produce one gallon of water, so to make 30 gallons, I will leave it running for 90 minutes.

Now, set several timers, so that you can check on the progress. In my case, I will set a timer for 30, 60 and 90 minutes from the time I start. It's very easy to get distracted, walk away and cause a flood.

There are some products in the market like the XP Aqua Flood Guardian which can help you prevent a flood by using a sensor that detects when the water reaches the desired level and automatically shutting off the water supply.

Add Salt

Now, get the bag of salt and a measuring cup and start adding salt to the water. It is best to sprinkle it rather than dumping it in to give it a chance to mix properly.

In this case, the instructions call for 1/2 cup of salt for every gallon, so I will slowly sprinkle 15 cups of salt, one at a time, into the water.

A message from the future

It turns out that 15 cups was way too much. We should've used around 9 cups instead but we're going to keep going with the original plan here so that we can learn how to fix it.

Throughout this guide, we will make mistakes but, rather than editing them out, we'll keep them and learn not only how to correct them but also how to prevent them from happening again.

  • If you have a powerhead or a water pump, you can place it in the trash can to do some of the stirring for you. You can also use an air pump with an air stone to oxygenate and stir the water.

  • I bought a small utility pump from Amazon which can be placed in the container without a hose to stir up the water for $26. It can also be used later, with a hose attached, to move the water from the container to the tank.

  • Or, you can do it by hand, using some implement to stir the water and keep it moving - just make sure it is as clean as possible and doesn't have traces of soap or other chemicals: our critters won't like any of those. You can buy a length of PVC pipe for this purpose and use it for nothing else.

In my case, I use a spare powerhead as well as the utility pump and let them mix for me. I add the salt slowly and then walk away for an hour or so. I then move the powerhead and stir up any salt that rests on the bottom of the trash can. I shine a flashlight into the trash can to check that the water is clear and the salt has dissolved completely - that there are no bits of salt resting on the bottom of the trash can.

Once this is done and before we put the water in the tank, we have to measure its salinity and possibly make adjustments.