Reefkeeping 101 - Water


Welcome to our “Newbie Corner,” a new column in Reefkeeping Magazine geared to the novice reefkeeper. We had discussed creating this new column among the editorial staff for some time and, because we had no volunteers, we drew straws and I got the short one. Anyhow, over the next several months I, and hopefully other more respected and knowledgeable people than I, will provide ideas, solutions and tips for the novice to marine aquarium husbandry.

Back in September of 2003 I started the New Tank Thread  and many new reefkeepers began using it as a guide. Although it's still helpful, it is getting a little long in the tooth in this ever-changing hobby. I'm going to start a new version right here on Reefkeeping, so tune in each month for what I hope will be a good guide to starting a reef tank.

Starting Out

One of the problems many novices face is that they currently have a 29-gallon tall tank with a mirrored back that’s full of about 60 African cichlids. The tank has been going well for them, and now they are ready to move on to saltwater fish. Anyone who has gone to the local pet store is easily dazzled by the brilliant colors of a saltwater angelfish, tang or maybe a wrasse. Pictures of wonderful tanks, ablaze with spectacular corals, can be found monthly in each issue of Reefkeeping.  Setting up a saltwater tank shouldn't be any harder than keeping cichlids, right?

Well, welcome to a different world. Although experience with freshwater systems is always valuable when entering the marine hobby, the two are entirely different worlds when it comes to tank setup and husbandry. The key to doing things right is to do research and formulate a plan. One of the first things to consider is deciding what type of tank you want. There are fish-only tanks that are free of corals and contain only invertebrates such as snails or perhaps some hermit crabs. Then, there are full blown reef tanks with lush growths of corals, anemones, clams and a host of other invertebrate species, with or without fish. Obviously, it is easier to set up and maintain a fish-only tank than a reef, and it also costs quite a bit less. Costs indeed may be a determining factor when developing any reef tank, and I will tell you up front they are far higher than those associated with a freshwater tank.

There are basic needs, however, for any marine aquarium. They are:

  • Water quality
  • Location and household utility services
  • Tank volume - type of tank
  • Lighting
  • Circulation
  • Filtration
  • Heating/cooling
  • Stocking
  • Feeding
  • Maintenance
  • Disease control

Now, as I said earlier, it’s wise to perform some research before even selecting a tank. Look over the many articles appearing in Reefkeeping Magazine and be sure to check out the Tank of the Month in each issue. Visit the “New to the Hobby” forum on the Reef Central message board. A sticky thread, posted by some deranged moderator (WaterKeeper), at the top of the forum points you to many threads that provide quick answers to common questions. The RC bookstore sells many books on the hobby. Also, and a very valuable asset to any new reefkeeper, there are various local reef clubs. Many of them have forums on Reef Central, so take the time to find one in your area and join.

Well, with that all said, let’s get on with it.  At the top of my list you’ll find the word - WATER.

No other component of your tank is more important and no other component needs to be adjusted and cared for as much as the water. Those African Lake cichlids live in hard water lakes, and those from the Amazon exist in soft, acidic river water. In either case, runoff from rainwater leaches through the soil and dissolves metals and organic compounds as it flows to the river or lake. Water quality is constantly changing, and freshwater fish have adjusted to these ever-changing conditions. This is not true in the sea. Conditions there barely change a hair from day to day and the water is amazingly pure. Metals such as iron, aluminum and zinc, usually common in freshwater, occur in the oceans in very small amounts indeed, typically 10 parts per billion or less. In fact, of those elements that are commonly regarded as heavy metals, only strontium, at 8 parts per million, is present in seawater in concentrations over one part per million.

Okay, I see a hand up in the back of the room. “WaterKeeper, you have to be joking! Seawater is loaded with salt and all those rivers carry those metals they pick up straight to the sea. How can you say that?” Well, for one thing the oceans are very large, but that only partly explains it, as all that dilution would be overcome in eons of time. The ocean also has the amazing ability to purify itself as the diverse biological population it contains process these materials and return them to the firmament from which they came. Now this won’t happen completely in your tank unless you have provided some ocean canyons over six miles deep, but the ocean has such conditions and materials that enter it are processed at great depths and, therefore, under great pressure. What all this means is that the creatures we collect in this hobby are acclimated to only exceedingly minor fluctuations in water conditions. A sudden change in the water’s chemistry, which a freshwater fish would handily shrug off, can be fatal to some saltwater fish, and even more so to sensitive invertebrates. And, it isn’t only metals that you have to watch out for; things such as nitrate also can be hazardous to your tank’s inhabitants. Those having freshwater tanks probably know that in the nitrogen cycle, toxic ammonia is de-toxified by conversion to nitrate in an ongoing process, but nitrate continues to accumulate. This also happens in a saltwater tank, but as these levels rise, corals and other invertebrates decline in health and eventually die.  For success in a saltwater tank we need to control the buildup of materials in the tank and maintain consistent water quality.

The first step to a successful marine system is to start off by using absolutely pure freshwater. “Hey, you over there!  Don’t you dare reach for that faucet!” I know that all of you have the finest tap water in the world, or at least your local utility tells you it is. Yet, in only a few cases (living by a glacially fed spring helps) will it meet the demands of a saltwater reef tank. You are going to need a water purification system, and you might as well resign yourself to getting one now if you want anything larger than a very small tank. These purification systems are called reverse osmosis (RO), deionization units (DI), RO/DI for short. They can produce water that is almost theoretically pure. Without getting too detailed here, reverse osmosis is a process that passes water under pressure over a semi-permeable membrane. The membrane acts like a very fine strainer, allowing mostly only water molecules to pass. Water leaving the filter’s reverse osmosis portion is typically 98% purer than what went into it. However, some molecules pass, such as dissolved silica, and the membrane will not stop ammonia at all. Enter the deionization portion. These work like a home water softener on steroids. They replace positively charged ions with hydrogen atoms, and negatively charged ions with hydroxyl, known by the chemical symbol OH-. The net result is that these form to make more water, and it is very, very pure. There are a few things to consider when buying one of these units:

  • The size of your tank
  • The type of RO membrane material
  • Your home’s water pressure
  • Your location
  • Water storage
  • The size of your wallet

As for tank size, if you have a 10-gallon nano system, you probably can get by using water from the local fish store or with distilled water from Wally World. On the other hand, a 200-gallon reef tank will almost always need an RO rated for at least 35 or, even better, 75 gallons per day. What? Yup, I’m saying gallons per day - not minute. One thing about the RO stage is they are not fast unless you have a multiple membrane model running at 200-400 psi. You don’t fire up the old RO/DI and fill a five-gallon bucket in a minute. Some of you may be wondering how fast the DI stage works alone. Well, that process is fast and a DI unit can easily make a couple of quarts in a minute. So then why have the RO stage at all? The answer is dollars. Running tap water into a DI unit eats resin canisters like crazy. They are too expensive when used in that fashion. The RO stage does 98% of the work, allowing the DI section to last 50 times as long as it otherwise would. We trade speed for $$$.

A typical RO/DI unit. The unit shown has a double DI filter (dark canisters on left). Photo courtesy of Skip Attix.

Membrane varieties come in two forms:  cellulose acetate (CA) and thin film composites (TFC). Cellulose acetate has the advantages of needing little pre-treatment of the tap water and being resistant to chlorine. Its drawback is that it is only about 90% efficient. The thin films need carbon pre-filters to remove oxidizing chemicals such as chlorine, and if chlorinated tap water reaches them, they deteriorate in short order. They also need more protection from particulates than CA membranes, so mechanical pre-filters are a must. However, they are 98% efficient, so the DI stage lasts close to five times as long as with their CA fed cousins. Because the prefilters don’t cost nearly as much to replace as the DI, you are always better off using a TFC unless there is a compelling reason not to.

Reverse osmosis units for home use are designed to run with tap water pressures in the range of 40-70 psi.  If your water pressure is much below that range, then you need to purchase a unit that has a booster pump. This reduces waste and speeds up the output.

Oh, did I say waste? I was saving that part for near the end because an RO membrane wastes around three-quarters of the water it processes. This waste flow carries the impurities that the membrane rejects down the drain and keeps the membrane’s surface from clogging. This is normal for all units, so you’ll need somewhere convenient for that wastewater to drain. A 75-gallon per day unit will waste roughly 225 gallons while producing that amount, so a drain is a must, although some people channel the waste to water their garden or fill a pond. One brand also passes this wastewater to a hot water heater for reuse. I recommend avoiding that because the wastewater is harder than the original tap water and, in hard water areas, it may contribute to scale formations on the heating elements. The other bit about location is the water storage part of the list. You can let the purified water flow into plastic trash cans if the unit is in a basement and occasional overflows are no problem. However, if it is under the kitchen sink (a popular location), then you’ll need to find a compact unit that includes an automated storage tank.

Last is the RO/DI unit’s price. Just like computers there are all types or variations of RO/DI units and they come with all sorts of bells and whistles. You’ll need a couple of carbon stages if your water is treated with chloramines, which are harder to remove than plain chlorine. Ask your water purveyor about what it uses for disinfection. Otherwise, a single carbon block is fine. As I mentioned, a booster pump is necessary if your water pressure is low. Automated systems that start and stop to meet demand are nice. Units containing a pressure gauge or two, one at the head of the unit, the other after the RO stage, are optimal. A built-in TDS meter (total dissolved solids), used to determine when the DI stage should be replaced, is always a plus, although a handheld meter will also let you judge the output water’s quality, usually more accurately than a built-in meter. Other than that it is up to you which options to add, but the average reefkeeper these days spends a little under $250 for a typical unit.

Yeah, I know.  We haven't even got these newbies a tank, and I’ve already told them the water system can cost close to three bills. I plan to really scare them just after Halloween when we talk about lighting, and by Christmas they will want Santa to put only rocks in their stockings.

Once we have a good source of pure water, we need to think about making it saltwater. If you live near a stretch of lightly polluted ocean water, then your worries are over. But we land-bound reefkeepers need to make our own. “What could be simpler?” you might ask.  “Everyone can get Morton's for a song. Heck, it even has iodine in it.”  We think of salt as sodium chloride, table salt; but, although seawater is composed mainly of this material, it has about seven other major components. And without those ingredients a tank will quickly fail. Science to the rescue! Marketed today are a host of synthetic sea salt mixes that can be reconstituted and used for your tank. You merely add water and the proper amount of salt mix, and you have a solution that pretty well resembles ocean water. They universally contain all the essential elements that Randy Holmes-Farley1


“Yes? Oh, it's you Harry. You know I hate it when you slip in here using that cloak of invisibility.”

“You can't fool us, WaterKeeper, and you just added a reference number so you can have an endless list of references at the end of this article.”

“But Harry, it won't look like a scholarly work without a reference table at the end.”

“We agreed at Hogwarts, before you started this series, that it would be simple and, to tell you the truth, you're no scholar as Dumbledore has repeatedly pointed out to you.”

“But I didn't use any magic spell words like obligate anaerobes or sexual dimorphism.”

“I just want you to watch your step and keep this simple.”

“OK, Harry and give my regards to Hagrid.”

“Bye. And finish this up soon; we have Quidditch practice at 4.”

Oh well, you can read Randy's article on seawater here.

Many synthetic salts are available, and all differ slightly, but all contain the essential components needed for a successful reef tank. They also eliminate the need to buy the many products sold that claim to contain the micro nutrients needed to keep a reef tank. Please don't add anything to a tank if you have no means to test for appropriate levels of it. Casually throwing something you know nothing about into a tank is asking for problems. As Harry would tell you, they are usually conjured up by “Dementors.”

Don't start making up salt solutions just yet; we have plenty more to do before that time arrives. Until then---read, read, read! See you next month...

If you have any questions or comments about this article, please visit this thread in the New to the Hobby forum on Reef Central.

Reefkeeping Magazine™ Reef Central, LLC-Copyright © 2008

Reefkeeping 101 - Water by Tom Murphy (aka WaterKeeper) -