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Coral Reef Keepers
1381 Plank Road Suite 98
Duncansville, Pa 16635

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Can I convert my freshwater tank to saltwater? PDF Print E-mail
Wednesday, 01 February 2012 00:00


Converting From a Freshwater to a Saltwater Aquarium

You've been amazed by the beauty of the fish and invertebrates and by the stunning variety of fish, crabs, shrimp and corals.  But you have a freshwater  (FW) aquarium and have probably thought about changing it to a saltwater (SW) tank.  Or maybe, you've decided finally to take the plunge.  Of course, you're wondering…how much new stuff do I need to buy?  How difficult will it be?

Chances are good that you already have much of the equipment you'll need to make the switch.  And making the conversion just isn't that difficult anymore.

You already have the following:

A tank and stand…..still usable

A heater…..still usable

A thermometer….still usable

A canopy (or aquarium cover)…..still usable

A light…..conditionally usable

Outsider filters/pumps…..stilll usable with some possible additions

Water conditioner….still usable

What you'll be needing:

Marine salt

Aragonite (your aquarium base)

Hydrometer (measures the concentration of salt in water)

Live rock

Other pumps, lights (optional)

Test kit


Let's talk about aquarium sizes first.  Here at Coral Reef Keepers we recognize that many tank sizes exist – the smallest nano tanks (typically 5 to 25 gallons), more typical sizes (29 to 75 gallons), big (100 to 450 gallons),  large (500 gallon-plus), largest.  (We're going to assume that you don't have a large aquarium that could double as a jacuzzi or a swimming pool in your house – at least, not yet.)  So maybe you're thinking, OK, let's start realistically.  Because the nano tanks can be rather touchy and unforgiving of poor water quality, we recommend them only for more experienced aquarists.

An aquarium ranging from 29 to 55-gallon makes a good beginning saltwater tank, largely because it has enough water to allow the aquarist a little more variety and some forgiveness for less-than-ideal water.

Here's something else you need to think about:  Will you want a fish only with live rock (FOWLR) tank?   Will you want a fish-and-coral tank?  Or will you want mainly corals with a few or no fish?  The answers to these questions point to the needs for better lights and pumps in your system, but you can add these at later times.

Next let's talk about water.  If you had a FW tank and tropical fish and if you used municipal water, you had to buy some sort of dechlorinator before you added the water to the tank.  If you have well water, you might have used some sort of water softening/metal/ion removing system.   If you've used dechlorinator, keep using it.   If you have a water softener, keep using it too.

Now, what about the saltwater itself?  Since saltwater fish, corals, invertebrates and algae live their lives in salt water, you have to provide good quality saltwater for them.  Luckily for us all, synthetic saltwater mixes were first introduced about a quarter century ago, so we now can have ocean-quality water in moments – literally by just adding water.  Remember:  You are creating the home for your fish, corals, etc.   Water quality is the single most important aspect of their lives and your success.

Let's talk about water conditions around a reef.  Extreme stability – almost without change – is its primary condition.  Replicating good quality water – with the proper salinity and pH, no nitrites, no nitrates, no ammonia, proper levels of calcium and trace elements – this is the aquarist's goal.

Is there a difference in the commercial salts that are available?  Definitely, yes.  And since water quality is so important to the life of the tank inhabitants, and the stability of the water (which in this case means no batch-to-batch variability) wouldn't it be important to know that chemicals in one batch of water you were adding to your aquarium were in the same concentration as the next batch?  And wouldn't it be important to know that the water had everything the aquarium inhabitants needed?   Again, the answers are yes.

For these and many other reasons, we use Instant Ocean.  While other brands are certainly available, we and many of our customers feel confident that the Instant Ocean provides the salt and trace elements in the right proportions that SW tanks need.  Importantly, Instant Ocean provides an assay (chemical analysis) of each lot.  More importantly, Instant Ocean has minimized its variability from batch to batch.

One aspect of SW aquariums is different from most FW tanks:  Salinity.  To measure salinity, you will need to buy a hydrometer that measures specific gravity (the concentration of salt per gallon).  While different species of fish and invertebrates require different salinities, most aquarists opt for a gravity around 1.022 to 1.024.  At this gravity, many species of fish and corals can co-exist in comfort.

Next, let's talk about lights.  Your FW aquarium also had some sort of light.  You may or may not be able to use it, depending on what kind of SW aquarium you want.  More on lighting later.

Finally, you also have some sort of filtration system – outside filter, canister filter, power heads, undergravel filters, etc.  You also probably have gravel or bottom material.   You will probably be able to use your outside and canister filters, but you won't need the undergravel filters or gravel any more.   Consider giving them to a friend who might like to start with a freshwater tank.

Instead of gravel, you will need some sort of material like aragonite.  Unlike gravel (which is chemically inert in a FW tank), the aragonite provides a source of calcium that helps maintain a pH of 8.2 in your SW tank.  Aragonite also provides carbonate buffer, strontium, magnesium, molybdenum, and potassium.   For readers unfamiliar with the term "buffer," a buffer is a chemical that keeps pH at or close to a particular level.

The aragonite bed also becomes a place where important bacteria make their homes, further adding to a stable chemical environment in your tank.

While there are various discussions on how much aragonite you need, we generally recommend between an inch and three inches per tank, or about one to one-half pounds per gallon.  How much is up to you.

Now, let's talk about filtration.  As you know, there are generally three types of filtration – mechanical, biological, and chemical – in a tank system.  If your outside filters circulate about 6 to 10 times the quantity of water in the tank per hour for a coral tank, that's adequate.   Tanks with fish require higher water flow, about 15 to 20 times the tank volume per hour, because fish generate significantly more waste.

The best way to remove the dangerous impurities – remove ammonia, nitrates, nitrites, and other water impurities?  Frequent water changes.

But another way is refitting the outside filter with Boyd's Chemipure.  Since you replace it about once every six months, it's significantly cheaper than carbon filters.  Boyd's also makes a Chemipure that will remove phosphates and silicates, those two primary contributors to brown and green hair algae in a tank.

But the real material that makes for a successful saltwater tank?  Live rock, that wonderful, formerly ocean material that contributes millions of beneficial bacteria to a SW tank.  Live rock helps cycle tanks and contributes mightily to converting toxic wastes into harmless ones.

We hope this helps you get started. Coral Reef Keepers is here to help you through every step.  Stop in, e-mail or call with any questions you might have concerning your switch to saltwater.


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