I have a 55 gallon tank that has been set up for a little over a year. It has an undergravel filter with two powerheads and an over the back penguin 330. These last two weeks I've had trouble with my ammonia level rising. I clean the gravel and do regular water changes. I asked the store and they recommended partial water changes a couple days in a row, didn't work. I have two larger eels, two Red Pacus, two Red Devils and a plecostomus in the tank. I've never had the ammonia problem before, is there anything I can do to get the level back down and what could be causing it?

The only reasons for ammonia rising in a tank that well-established are:

1) The fish have out-grown the tank, which is quite possible with Pacus, as that species requires a minimum tank of at least 150 gallons, larger would be better. If the Pacus are about 8 inches in diameter, they have gotten too large for the tank and should be removed.

2) You are over-feeding. Again quite possible given the messy nature of the fish you keep.

3) The tank is under-filtered. With those fish, you should be running an undergravel filter and a large canister filter such as an Eheim 2215 or Eheim 2026. The power filter you have has reached its limit.

4) Any combination of the above.

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What is the nitrogen cycle?

The nitrogen cycle is the same all over the planet. It is simply the oxidation of organic compounds made primarily of nitrogen and hydrogen to simple compounds composed of nitrogen and oxygen. The end results of the cycle as it occurs on Earth are nitrates which feed plants and algae, and nitrogen-based gases which enter our atmosphere where they are recycled to repeat the entire process. Most of the air we breathe is nitrogen, not oxygen.
The process is the same in an aquarium, but the end results are much different. Fish produce ammonia as waste. Several species of beneficial aerobic (oxygen using) bacteria living in the biological filter consume the ammonia. Using oxygen, they convert the ammonia through a series of steps into nitrates. Nitrates are used by plants and algae as food. In an aquarium, that is usually the point where the nitrogen cycle gets rudely interrupted! Algae is unsightly but beneficial. When it is completely removed from an un-planted or non-reef aquarium, the end result is high nitrates which must be removed through water changes.
Most aquariums are closed systems. There are the legendary so-called "balanced" aquariums that never require water changes. The word "balanced" here, refers to a system where the nitrogen cycle can actually complete itself, so the cycle is balanced. Examples of these would be: 1) a freshwater aquarium with a lot of live plants and a few fish; or 2) a saltwater live-coral reef aquarium with a lot of photosynthetic corals and sessile (fixed) invertebrates and a few fish. The object of setting up a "balanced aquarium" is to duplicate the same ratio of plants (or photosynthetic corals) to fish that would be found in the wild. It's a great idea, but most aquarium owners would not be satisfied with the results. There are hardly as many fish anywhere in the wild, per cubic foot of water, as there are in an aquarium. Keeping a balanced aquarium means not having a lot of fish. Keeping an unbalanced aquarium means we can have lots of fish, but we have to do water changes and change filter material to keep all those fish alive.
Newer natural aquarium methods utilize anaerobic bacteria to complete the nitrogen cycle. These facultative-anaerobic bacteria consume nitrates as part of their metabolism and convert them to nitrogenous gasses which escape the aquarium from the water surface. Most of the fish-only aquariums we've seen defy the nitrogen cycle as it occurs in nature. Too many fish are kept, and that problem is addressed by over-filtering the water and frequent water changes. Rather than cultivate it, algae is removed that grows as nature makes an effort to "balance" the system. In these aquariums, the cycle does not complete itself. The drawing to the right illustrates the effect on the nitrogen cycle in a so-called "sterile" aquarium with no living plants or algae. When selecting an aquarium, we recommend a balanced system, such as a planted freshwater tank or a marine reef tank. The rewards are greater, and these aquariums are less expensive to maintain.

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What is Redox potential? Do I need to worry about it and if so, how do I control it?

Let us start by saying that redox potential is really a saltwater thing, so if you have a freshwater aquarium, read on because we'll explain this soon, or . . . because you like the way we write. In our humble opinion, the redox potential of a marine aquarium is one of the best measures of success in maintaining a great saltwater environment. If we had our way, every salt tank everywhere would be equipped with a redox meter (ORP meter).
We'll start with our very own anthropomorphic, unique, over-simplified and only-partially-correct definition: "The redox potential of an aquarium is a measure of the aquarium water's ability to cleanse itself." Now here's the long chemistry-lesson version. You'll soon understand why we gave you the simple version first:
With the exception of energy, everything, everywhere, that's anything at all, is composed of atoms. An atom, you may recall, is composed of protons, neutrons and electrons. The protons and neutrons form the center of the atom, called the nucleus. Protons carry a positive charge, and neutrons are neutral, so the nucleus has a positive charge.
There is one negatively-charged electron for every positively-charged proton in an atom. The electrons circle the nucleus in layers or shells. It is the electrons in the outer shell that "react" with electrons in other atoms to form compounds.
The more protons an atom has, the heavier it is. Atoms with different atomic weights are known as elements. When two elements combine in a reaction, they form a compound. Compounds may exist as molecules or ions. Molecules are un-charged components of a compound. Ions are either negatively or positively-charged components of a compound. The simplest molecules are two combined atoms of one element, for example, oxygen as O2, or chlorine as Cl2.
"Redox" is short for oxidation-reduction, which is a type of chemical reaction. A redox reaction occurs when two elements combine, and one element "loses" an electron to the other element. The element that "loses" an electron is said to be "oxidized." The element that "gains" an electron is said to be "reduced." By the way, the electrons aren't really lost. They're shared in such a manner that the resulting molecule has an electrical charge. For example, when two sodium atoms (Na), and a chlorine molecule (Cl2), combine to form two molecules of table salt (2NaCl), they undergo a redox reaction. The sodium is oxidized and "loses" an electron, so that it has a positive charge. Chlorine is reduced and "gains" an electron, so it has a negative charge. The two go hand-in-hand. If one element is reduced, another must be oxidized.
Some atoms, like chlorine (Cl) and oxygen (O), really "want" to "gain" electrons. These atoms are called oxidizers. Some atoms, like sodium (Na) and Hydrogen (H), really "want" to "lose" electrons, and are called reducers. Water is an amazing molecule. It too, is formed by a redox reaction, which forms a bi-polar charged molecule, having a positive charge on the hydrogen end and a negative charge on the oxygen end, making it both an oxidizer and a reducer at the same time.
"Potential" refers to the charge of an ion created a redox reaction and dissolved in water. When table salt (NaCl) is dissolved in water, it forms two ions. One is an oxidized positively-charged sodium ion, (Na+), called a cation (+). The other is a reduced, negatively-charged ion, (Cl-), called an anion (-). The oxidation reduction potential of saltwater is the measurement of the total cations and anions in solution that are available to either oxidize or reduce other molecules. Redox potential is measured in millivolts (mV). If there were an equal amount of cations and anions dissolved in a given volume of seawater, the water would have a redox potential of 0.0 mV. Water in an aquarium has plenty of free oxygen in it (we hope!). Oxygen is a great oxidizer, and is busy "stealing" electrons, so there are always more positively-charged (oxidized) cations present in clean seawater. Therefore, saltwater in an aquarium will have a positive redox potential. The ideal redox potential in a marine aquarium is between 350.0mv and 400.0mv.
If the oxygen levels drop in an aquarium, more anions appear on the scene, and the redox potential will fall. This happens as organics accumulate in the water, reducing oxygen. If a strong oxidizer, such as ozone (O3), is introduced, the concentration of cations increase, and the redox potential will rise.
By measuring the redox potential of the water in a marine aquarium, we can tell how clean the water is. A redox potential meter only measures redox potential. A redox meter/controller not only does this, it also can be set to maintain a desired redox potential by controlling an ozonizer which doses ozone into the water, usually inside a protein skimmer or an ozone reactor. Ozone is such a powerful oxidizer, that caution should be exercised when using it. It is also used in aquariums to control un-wanted pathogenic microorganisms and parasites.

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I notice that the pH of my aquarium seems to drop at night and rises during the day. Why is that and what can I do?

This is a natural phenomena and you shouldn't and can't do anything about it. You didn't mention if you had a freshwater or saltwater tank, or what type of aquarium you have, but we're guessing that, regardless of whether you have salt or freshwater, you do have either zooxanthellae-host invertebrates, algae or plants in your tank. Something in there is photosynthetic, or the variation would probably not be pronounced enough for you to measure much of a difference.
Photosynthetic organisms include plants, many algae and some cyanobacteria. These respire during the day by photosynthesis, taking in carbon dioxide (CO2) and releasing oxygen (O2). At night however, they do just the opposite, taking in oxygen and releasing carbon dioxide as we do. As all this carbon dioxide is released, it reacts with hydrogen ions in the water to form mild carbonic acid (H3CO3), which lowers the pH of the water. When the lights come back on, carbon dioxide is taken up by the plants and/or algae, which reverses the reaction that formed the carbonic acid, and the pH rises again. Incidentally, many anaerobic decaying bacteria also release CO2 as a by-product of their metabolism.

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I tested my water and found low levels of ammonia. What happened and how can I correct this?

If this is a relatively new aquarium which has had fish in it for less than three weeks, this condition could be normal. Otherwise, either something is dead and decaying in your water, or you have done something to your aquarium which resulted in a loss of a substantial population of nitrifying bacteria.
Most bony fish produce nitrogenous waste in the form of ammonia (Most sharks, skates and rays produce urea as we do). Ammonia can also be produced as a by-product of the decay of detritus or dead specimens left in the tank.
In an aquarium, beneficial bacteria cultivate, usually in a filter or in the gravel, that oxidize the ammonia, first into nitrite, and then nitrate.
A new aquarium begins with no bacteria, so an ammonia test would yield positive results until a bacteria population exists that is large enough to handle ammonia production. If this is the case, time will heal this situation.
If a major portion of the bacteria population is removed, an ammonia test will yield positive results. This could happen, for example, by removing the gravel in an under gravel-filtered aquarium and washing it in tap water, or changing the filtration media in a wet/dry filter. If this is the case, you can try adding some ammonia neutralizers and/or commercial bacteria cultures. You can also try to obtain some established gravel (or live rock or sand for marine tanks) from another aquarium. Water changes will not help, and may make the situation worse. If these methods fail, all you can do is cross your fingers and wait for the bacterial population to bounce back. Luckily, nitrifying bacteria multiply very rapidly. If the cause of the ammonia rise is due to decay, it is important to find the source of ammonia production and remove it immediately. Dead fish left in the tank are likely culprits. After removing the dead material, a partial water change should bring conditions back to normal.

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What is pH and how can I control it?

pH is a measure of positively-charged hydrogen ions (H+) and negatively-charged hydroxyl ions (OH-) in a given substance. The more (H+) ions there are relative to (OH-) ions, the lower the pH value, which makes the substance acidic. The more negatively-charged (OH-) ions there are relative to (H+) ions, the higher the pH value, which makes the substance alkaline. The pH scale ranges from 1.0 to 14.0. When There are equal quantities of (H+) and (OH-) ions in a substance, the pH will be 7.0, or neutral. Pure water has two (H+) ions (H2) and two (OH-) ions (02), forming (H2O), so it is neutral.
The pH in aquariums may be controlled through the use of buffers that either raise or lower the pH. Decay of detritus and the accumulation of nitrates and phosphates in an aquarium will naturally lower pH. Partial water changes, done on a regular basis, help to control this process.
The pH of most freshwater aquariums is between 6.5 and 7.5, depending on the type of aquarium. Typically, we do not recommend changing the pH of most freshwater aquariums unless it is a live-plant aquarium or a specialized aquarium for African Cichlids, Discus or other Amazon basin fish, or unless you are trying to breed a particular fish that will only breed at a certain pH value. Most freshwater fish available in stores today are bred in the same hard, alkaline water that comes out of our taps, so there is no need to adjust pH for them. Lowering the pH of hard, alkaline water is difficult anyway, as the hardness in the water will only raise the pH again. In live-plant tanks, the decay of dead plant material tends to naturally acidify water. If you have set up a specialized freshwater for fish that require soft, acidic water, you should use reverse osmosis or distilled water so that you can safely control the pH of your tank.
The pH of most saltwater aquariums should be between 8.0 and 8.5. Saltwater aquariums are naturally alkaline from buffers found in most high-quality salt mixes. By doing a partial water change on a regular basis and vacuuming the substrate, you can usually maintain the pH without additives. Over-stocking and over-feeding the aquarium can increase the amount of dissolved organics in the tank which will lower the pH. In marine reef aquariums, the use of reverse osmosis water is popular. Reverse osmosis produces very pure water which is slightly acidic and should be buffered when doing a water change.

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What can I do to raise the dissolved calcium level in my living-reef aquarium?

To truly understand how to maintain good dissolved calcium concentrations in seawater, it is important to understand the relationship between pH, alkalinity, carbon dioxide, carbonate hardness, and calcium carbonate, which are some of the basic components used in the natural buffering system of saltwater. Advanced aquarists may sneer a little at this over-simplified and partially incorrect explanation, to which we would say: Hey! send us your best simple explanation, and we'll post it and give you full credit (but remember to keep it very simple - Aha! . . . not that easy, is it?).
A simple way of looking at it is to examine only the relative relationship between pH, alkalinity and calcium. Seawater has a relatively high pH of approximately 8.2. At a high pH, calcium does not tend to dissolve well. If you add a lot of milky Kalkwasser to a tank with a normal pH value, some of the Kalkwasser will precipitate and settle out as calcium carbonate. In most marine tanks, the pH has a natural tendency to fall over time. This is due to the accumulation of dissolved organics that form mild acids, and the production of carbon dioxide by algae.
As pH drops, the mild acids dissolve calcium carbonate (from coral gravel, shells or precipitated calcium in the tank), releasing calcium into the water, so calcium levels rise. As pH drops, total alkalinity also drops.
So this presents us with a catch-22 situation. Unfortunately, to maintain a perfect calcium level (most authors agree on a value of 420 ppm or higher) all the time, we would have to maintain a pH in the aquarium of about 7.6, which is dangerously low for the animals we keep. So the solution is to maintain a pH that is too high to naturally dissolve calcium and add calcium supplements to the aquarium. When we add calcium to the water, alkalinity tends to drop, so it is important to buffer the water as well. This is a balancing act that many reef hobbyists face.
The best (and most expensive) way to add calcium to a reef tank is by using a calcium reactor. It is usually better to add calcium at night when the lights are off and pH is naturally falling. Most folks use Kalkwasser, which is powdered calcium hydroxide. This may also be supplemented with liquid calcium chloride. There are several schools of thought on the best way to add Kalkwasser to an aquarium. Mixing the powder with warm tap water yields a milky solution that will really do a great job of raising calcium, but this should be added with caution as it may also boost pH to dangerously high levels. Allowing the milky solution to settle, yields a clear "lime water" solution that doesn't maintain calcium levels as well, but still does a fair job without a drastic rise in pH. Clear Kalkwasser solution or calcium chloride may be drip-lined into the aquarium or added on a daily basis. Add buffers in the morning to help elevate the alkalinity. Another great product that adds calcium and buffers the water at the same time is C-Balance® by Two Little Fishies®. Always test calcium, pH and alkalinity before and several hours after adding calcium so you can note the effects of calcium addition. This will also help you to better understand the saltwater buffering system.

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My sink has an RO system installed into it. I would like to use water from the RO system to fill my aquarium. Should I add any minerals to the RO water?

Reverse osmosis (RO) water should be replenished with ionic forms of minerals and salts before use in most marine and some freshwater aquaria, using a preparation designed for the purpose such as Kent marine RO Prep or RO Right. RO Prep is for use in water used for saltwater tanks and RO right is for use in water used for freshwater tanks. The one exception to this is RO water used for aquariums for soft acid water-loving fish such as Discus and other sensitive fish that come from tropical rivers and streams. With these types of aquaria, it is better to leave the water un-treated, except perhaps with a little buffer or Blackwater treatment. Distilled water on the other hand, should always be pre-treated before use.

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I have an acrylic tank. After I fill it, the front and back side of the tank started to swell quite a bit. It was flat before and now it looks like an arch in the front and back. Is this normal?

There are acrylic tanks, and then there are acrylic tanks! In almost any acrylic tank, depending on the manufacturer, some slight bowing may occur, but it won't be noticeable. If the tank is designed properly, bowing will only happen in the back panel. Excessive bowing comes from using material that is too thin. Major manufacturers use thicker acrylic and that is why their tanks are more expensive. While it may be a risk, acrylic is still much stronger than glass. The aquarium is probably not going to explode, or break. It may actually hold water for many years in that condition. Signs of weakness include air bubbles or pockets forming in the seams, and "crazing." Crazing is a term sued to describe horizontal stress lines that begin in the corners of the tank, and spread out from there. They look like thin cracks in the acrylic, but they're actually caused by stress of the molecular structure of the plastic. When crazing spreads several inches out from the corners, it is probably time to replace the tank. Acrylic tanks that are well-made will always be superior to glass in nearly every respect. Don't let a bad experience with a poorly-built tank steer you away from a good brand of acrylic aquarium.

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I have a 75 gal saltwater aquarium with an A-miracle SL150 trickle filter. It uses a Mag-Drive submersible pump that keeps stopping. I think I need a replacement. Is there anything I can do with this pump, and if not, what pump would you recommend?

We might be able to save you some money. Have you taken the Mag Drive pump apart to look at the impellor? In case you haven't, here's some instructions. You unscrew 4 screws on the face, then gently pry off the pump volute from the face of the pump using a flathead screwdriver. Remove the impellor and examine it. If you are using an Amiracle filter, you may be using the filter felt sheets for the trickle plate. Small filaments from this felt may have gotten caught in the impellor blades and are making the pump stop. Clean the impellor thoroughly and the impellor well, and reassemble the pump. If the pump still malfunctions, we would recommend a Mag Drive 7 for a replacement.

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Frequent Aquarium Questions