Reefkeeping 101 -
Bogus Information

As a master of bogus information I see many threads where old wives' tales are still presented as valid answers to posted questions. Much of this mis-information has been touched on in previous columns. Iíll highlight some of the most common this month.

Water Changes Prolong the Cycle

This myth is so widespread that even experienced reefers believe it. People that hold to this concept seem to believe water changes remove beneficial bacteria swimming in the water column, and thereby water changes remove the bacteria you want.

While it is true that some bacteria are carried about in the water column, for the most part, bacteria do not swim in the water. If we could count them we would have several million floating around in a small tank. However, bacteria carried in the water are only a tiny portion of the overall bacterial population of a tank. The bulk of the bacteria in any tank are sessile, meaning they are attached to solid objects in the tank. A single grain of sand may have a million bacteria growing on it but those lost to water changes are very small compared to the total numbers in the biological film.

In a new tank, we are adding live rock and possibly live sand that has this biological film covering it when it is received. It is all the population that the tank will need. If the rock is curing there is an abundance of dead and dying organisms on the rock. Most of the die-off consists of sponges and other organisms that didnít survive the trip to your tank. As the rock cures beneficial ammonifying bacteria feed on the nitrogen released by decaying organic matter and multiply at astonishing rates. A single bacterial cell may become 64 in less than a single day. Since the bacteria that turn protein into ammonia reproduce faster than those that consume the ammonia and change it to nitrate, ammonia levels climb. Ammonia levels reach toxic levels in fairly short order and surviving higher organisms on the live rock die.

This is a time to for large, frequent water changes. The water change helps remove ammonia, and other decay products from the tank, and helps the tank achieve equilibrium in which ammonia can be processed to nitrate almost as soon as it forms. It lowers the numbers of organisms that will be lost on the rock as it cures. Sure, the water changes also remove some small number of beneficial bacteria from the tank but there are far more attached organisms on the live rock and sand than are needed in the first place. The lost bacteria have no bearing on the time cycle will take and the following algae outbreaks will be shorter in duration as their will be fewer nutrients in the water column to help fuel the algae growth.

Do yourself and your new live rock a favor and do at least 25% water changes every day on a cycling tank. Even larger water changes are perfectly fine and probably will shorten, not lengthen, the cycle period.

Carrying a Slightly Lower Salinity in the Tank Lessens Disease

This bogus information seems to be perpetuated by the pet shop trade. The exact source of the myth is unknown, but it seems to have started in the early 1980s. I have been told it may have originated in an article by Herbert Axelrod, but cannot confirm. No matter, the concept that keeping a marine aquarium at lowered salinity, with specific gravity of ~1.019, is commonly cited as helping to prevent disease outbreaks in saltwater fish.

This idea has never been proven to help fish in any way. A specific gravity of 1.019 is far short of the level of 1.009 needed to combat ich during hyposalinity treatment. The practice may save some money for the fish supplier in it requires less salt, but it does not prevent disease. Although it doesnít seem to hurt fish, lowered specific gravity is not good for corals and other invertebrates. They need to be maintained in the range of 1.025-1.026 for long-term health and well being. The widespread use of low salinity husbandry is why one needs to carefully acclimate new fish. If the fish is maintained at low salinity at the fish store, a sudden change in salinity can be damaging to the fish.

Packaged Live Sand

Shop around for live sand and you will find all sorts of bagged wet sand, with the claim that it contains live bacteria, and is great for deep sand beds. The good news is many are aragonite sands but the downside is the few bacteria added donít have nearly the biological diversity of a true live sand bed. This packaged material contains a few strains or bacteria, usually nitrifying bacteria, but in no way duplicates the many forms of bacteria found in naturally harvested live sand.

It also lacks the higher organisms that make sand truly live. Organisms like protozoa, copepods, worms, microstarfish and mini sea cucumbers are present in true live sand and help keep the sand bed healthy. It can be argued that many of these organisms will be on the live rock and they will soon seed the sand. Some are present on live rock but it is a different environment than is found in an ocean sand bed and important sand dwelling organisms are not present on the rock. If you want a good deep sand bed then it is important that at least part of it be true live sand and not artificially seeded sand.


I donít know why I donít market my own ďmagic potionsĒ as supplements for marine tanks. A few chemicals, cheap balance, plastic bottles and a catchy label and I too could cash in on a reef gold mine. There seems to be a supplement on the market for just about every major, and many minor, ions in seawater. Now donít get me wrong, some are beneficial like those used to boost alkalinity or calcium, but many are not needed or, if they are, we have no idea at their rates of depletion in a marine aquarium. Iím not sure but I may have coined the phrase, ďOnly add things that you can testĒ. Some additives, such as iodine, may do more harm than good. There is no reliable iodine test that can be used for making additions. It is truly hit or miss.

In almost every case water changes will replenish minor elements lost by biological uptake. Even strontium, needed for stony coral building, is present in the salt mix and a simple water change recharges any that is lost. If you add a supplement, do so for only calcium, magnesium, alkalinity and possibly pH control. The rest of the supplements should not be needed if you do regular water changes.

Hermit Crabs

I think these guys must have a strong union because people are told to add a crab per gallon or someone will break your legs. Iím guilty of falling into this trap and throwing several dozen into my tank. Shortly thereafter I wondered what happened to all the copepods and bristle worms in the sand bed.

Hermits are great scavengers but many are also vicious predators. Load the tank up with hermits and pretty soon there will not be many wee critters living in the tank. Even larger things, like snails and fellow hermits, will begin to be eaten. They are fun to watch but avoid having more than one or two in a small tank and a handful in a large tank. Be sure to research the species, as some are more predatory and damaging than others.


These days any hood on the market seems to have moonlights included. Hey, watching a moonlit tank may be romantic but that is about it. The initial reason people started using moonlights is that corals follow a fixed pattern of reproduction that is related to the lunar phase and duration. It seems to be a biological time clock for coral spawning. However, Iím not truly convinced about that light alone is the trigger. My own feeling is that the gravitational attraction of the moon creates a tide pattern that the coral recognize and that the lunar photoperiod is probably secondary.

UV Sterilizers

Not a myth, as they do work, but somewhat questionable for use in a home tank, is the UV sterilizer. They do work as advertised and can kill bacteria, algae and protozoa; it is a ciliated protozoan that causes ich. The main question is, do they prevent disease in the tank? In the display tank, disease prevention is highly unlikely unless the unit is extremely large. The filtration rates for common units are usually not high enough to kill a significant number of organisms to prevent infection. They also kill off protozoa that are food for corals and copepods.

UV sterilizers can be useful under specific circumstances. In the case of multiple tanks connected to a common sump, a UV sterilizer placed in the return line to the displays can provide a barrier against disease moving from one tank to another. In this case, all the water is exposed to the UV light and the discharge water will be almost pathogen free. Another use is in the quarantine or hospital tank. These tanks are generally small and the use of a UV can help remove many pathogens. This is especially true if dip methods are used to control the disease, a UV sterilizer can kill emerging parasites not killed by the dip.

For a large display tank there are better uses for your money. A canister filter with a micron cartridge can filter far more water and remove more pathogens than a UV. They also cost less than many UV sterilizers. I donít advocate the full time use of a canister unless the filter element is cleaned at least weekly, but in an infected tank it will usually do a better job at removing disease causing organisms.

Activated Carbon

There has been a great debate for years on whether one can/should run activated carbon in a reef tank. The anti-carbon argument takes the position that carbon removes beneficial material that coral and other inverts consume. I have never heard a convincing explanation of what this supposed food consists of or what it does for these organisms. Carbon is used to remove dissolved organic compounds from the water. The effect of DOCs could be to merely cause the water to take on a yellowish appearance they can consist of complex organic toxins produced by the creatures in the tank. Dissolved substances are not directly absorbed by higher animals and are mainly consumed by bacteria and algae. Coral, anemones and similar critters donít directly consume dissolved organic materials. The zooxanthellae in corals donít benefit much from dissolved organics as they get their nutrients directly from the coral and the uptake is extremely fast. It is highly unlikely that running carbon 24/7 removes any material that is essential to the livestock in a tank. Carbon improves water quality and reduces bioload on the tank, so I would say to go ahead and use it.

Well, those are a few of the bogus bits of information that circulate on the web. There are others but I think these are the most common. Until next time, dear readers.

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

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Reefkeeping 101 - Bogus Information - by Tom Murphy (aka WaterKeeper) -