Many times you hear that brackish water fish probably do best with about one Tablespoon of salt per five gallons of water, or do they?

I have an idea of my own that many brackish water fish do best, when the salinity varies. If your aquarium has no salt, add one Tablespoon of Aquarium Salt per each five gallons of water. Your 125 gallon aquarium would get 25 Tablespoons of Aquarium Salt. This will change the salinity from 1.000 to less than 1.001, which is a small increase.

Twice a week remove 20% of the water, which will be 25 gallons in your aquarium, and replace it with fresh tap water from your faucet. After three weeks of changing 20% of the water twice a week, add 25 Tablespoons of Aquarium Salt again, and repeat this process every 3 weeks or so.

By doing this the salinity will increase slightly, when you add the Aquarium Salt, then go back down to almost 1.000 after the six water changes over the period of three weeks, and then back up again, when you add Aquarium Salt again.

When you add the Aquarium Salt, the salinity increases abruptly, and many pathogens such as bacteria are killed by that change in salinity. The fish feel some stress too, but not too much. Click here to read more about how Aquarium Salt works to kill pathogens.

You're probably wondering about your other fish like your Clown Loaches. We've tested Aquarium Salt on all the fish that we sell, and up to one Tablespoon of Aquarium Salt per each five gallons of water will not harm them. The change in salinity will often help them.

I haven't read this advice elsewhere, and for the most part I try to give advice on this web site that is well established, but in this case I'm giving you my method, and I hope it helps you.

First of all I miscalculated, when I wrote 1.003. Actually, when you add one Tablespoon of Aquarium Salt to five gallons of freshwater the salinity goes from 1.000 to slightly less than 1.001. I have changed the page on this web site that used to say 1.003. Thank you for helping me correct that number. I apologize for my mistake.

I was interested to read that your Brackish Water do well for you at a salinity of 1.010 to 1.018. I have read recommendations elsewhere of between about 1.005 and 1.006, but several of these recommendation were posted by people that we know just to be writers, who we know, and they have proven to us many time in the past that they are  terrible fish keepers.

These folks also strongly recommend using sea salts because "it makes sense." Unfortunately we have learned that some things that make sense, don't work when actually tested.

Now about the salts. The world's oceans are full of seawater that contains a variety of salts, including sodium chloride, potassium chloride, magnesium chloride, calcium chloride, calcium carbonate, calcium sulfate, and many other salts. Ocean water contains about 3.7% solids by weight, and about three-quarters of the solids is sodium chloride.

In stores you can buy,

(1) Table Salt, which is nearly pure sodium chloride to which is added some iodide to prevent goiters in people and some silicates to prevent the salt from caking. This salt is not recommended for use in aquariums, though some people have reported using it and claimed it has not hurt their fish.

(2) Rock Salt, which is often produced by evaporating the water from ocean water. Rock Salt is about 98% sodium chloride and is usually sold in bags for use in water softeners.

(3) Salt Pellets, which are bright white. The material in these pellets comes from salt mines and is suppose to be almost pure sodium chloride.

(4) Aquarium Salt, which is available from most stores that sell pet fish. This salt is mostly sodium chloride and is labeled for use in aquarium.

(5) Marine Salts Mix is sold in stores that sell Marine Fish. Marine Salts Mix contains nearly the same mixture of various salts that naturally occur in the oceans. If you add these salts to distilled water, the resulting solution will have a pH of over 8.0, which is quite high for fresh water fish.

We use and recommend (4) above, which is Aquarium Salt that is labeled for use in aquariums. We have found in our facility that one Tablespoon of Aquarium Salt added to each five gallons of our tap water produces the best water for the Brackish Water Fish in our facility.

As you mentioned most of the Brackish Water Fish in our facility are young fish that are less than 2.5" long, and we speculate that generally young brackish water fish prefer water with less salt.

I don't know what the effects of the Aquarium Salt would be on your live rock, and I have never owned any live rock, but I would guess that the live rock should be kept in water with a concentration of about 1.025 of Marine Salts Mix that are listed above as (5).

You would have to add about five Tablespoons of Aquarium Salt to five gallons of water to get a salinity of 1.003.

I just removed my mistake about the 1.003 from the other pages in this website. Not to hide my mistake, but to avoid confusing more people and wasting their time trying to make sense of the 1.003 like you did.

if you add 1 Tablespoon of Aquarium Salt to five gallons of freshwater, you probably won't be able to see the small change in salinity from about 1.000 to less than 1.001 on your hydrometer. So hydrometers are not accurate enough to be useful for measuring these small amounts of salt.

In our facility we have a Hanna TDS Meter that can measure these smaller amounts of salt. Click here for more information about this meter.