Keeping an Octopus in a home saltwater aquarium.

I have kept brown and even poisonous blue ring (I do not recommend Blue ring) octopii.
In fact a brown octopus was one of my first saltwater creatures back in the mid 1970s.
They make great pets and are highly intelligent, in fact mine would recognize me and come to the top and stick its tentacles out to take food directly from me.

Here are a few points to keep in mind though:
*An Octopus will squirt ink they squirt when frightened, but that is rare. Try and keep a peaceful environment and this will not become a problem.

*The Blue Ring Octopus from the Great Barrier Reef is one of the most toxic animals on earth with its neurotoxin. A bite can kill in under an hour (although they very rarely bite).
These Octopus prefer the warmer waters that most home aquariums provide however the poison problem I think over rides this plus (even though I have kept them).



Here are some important points for success in keeping a Brown Octopus vulgaris and bimaculoides:
*They are cold water preferring so an aquarium under 75 F is best (under 70 F is better).

*They need crab or other crustaceans in their diet. Along this line they will consume cleaner shrimp, coral banded shrimp and similar

*They are sensitive to nitrates above 20 ppm. So good filtration (such as the Berlin Method which includes live rock and possibly a Mud Filter is a must). Along the line of anecdotal comments I have read statements that a Protein skimmer is a must; not true! (Although the use of a Protein Skimmer certainly helps keep the odds of a healthy aquarium in yours and your octopus' favor). I have kept many a healthy Brown Octopus without a protein skimmer, the key is low nitrates and a healthy environment (which includes Redox Potential) and if a Protein Skimmer is part of this plan, fine, however there are other good methods as well. If anything the benefits obtained by a UV Sterilizer (although different benefits) would be more important.

*They have short life spans, often under two years and a warm aquarium will shorten this further. Also do shorten it further by easily escaped from loose fitting tops.

*They do NOT mix with eels (mortal enemies)

For further reading about Octopus intelligence, please read this article from the Washington Post:
Brilliant Houdinis of the Deep

Updated 12/26/09

Although less toxic than ammonia and nitrite; nitrate (NO3) as a nitrogen compound also causes stress at all levels making a fish’s organs work harder to adjust to it’s new environment, especially at levels higher than 100 ppm). The increasing stress results in the loss of ability to fight diseases, the ability to heal itself, and the ability to reproduce.
It is essential for you, the aquarium hobbyist, to maintain a proper environment for your aquatic companions. High nitrate levels are a sign of poorly maintained aquariums and will cause problems in the long term (I recommend levels under 40 ppm for FW, 20 ppm for Saltwater fish, & under 1 ppm for reef).

Nitrates are potentially dangerous due to the effects on the water chemistry and on a healthy environment for your fish while nitrates are accumulating. The higher the nitrate levels the higher and severe the consequences due to the stress on your fish and the favorable conditions for a serious algae outbreak.
Nitrate levels around 5 ppm or less are found in nature which provides an almost nitrate free environment (although a Nitrate level of around 15 ppm is usually best for planted freshwater aquariums). The higher the nitrate concentration the more stress for the fish. Extremely severe stress is reached at levels exceeding 100 ppm. Many plants will fail before reaching this level, this due to an accumulation of life forms such as detritus worms feeding on decomposing waste, and the consequently higher biomass (organisms living in the aquarium) leads to an increasing demand of oxygen.

I will also add that although nitrates are not dangerous in the short term unlike ammonia or nitrites; in established tanks I usually test this parameter more often as this is a good indicator of how well I am doing in my tank cleanings (if enough water is being changed and often enough). Tests of KH & GH are also useful in indicating an established tanks health.

One more point about nitrate; I have tested the water on under sized aquariums /bowls containing otherwise healthy goldfish. The nitrates would often exceed 200 ppm! These goldfish (although they appeared healthy), rarely lived more than 3-5 years as compared to the 12 + years of the goldfish I have kept for clients in pond and larger aquariums.
University studies in Cattle show nitrate levels in water over 221 ppm to be harmful or even fatal, so I sure would NOT want my fish kept at nitrate levels approaching this number.

*WHAT ARE NITRATES?

Nitrates (NO3) are compounds composed of a nitrogen and three oxygen atoms and are often the final stage in the nitrogen cycle of fresh and saltwater aquariums if there are not nitrate removing plants, algae, or nitrate reducing anaerobic bacteria present. Nitrates are the conjugate base (chemical substance that releases a proton in the backward chemical reaction) of nitric acid (HNO3), consisting of one central nitrogen atom surrounded by three identical oxygen atoms. The presence or production of large amounts nitrates can result in the presence of Nitric acid according to the Brønsted-Lowry theory of acids and bases which will in turn affect an aquariums pH and KH (which can result in dangerous pH swings).

Large amounts of organic mulm and decomposition in an aquariums (or pond) gravel or in filters is often a common cause of persistent nitrate problems. Another clue to this is a pH that tends to drop quickly, often even with buffers added (assuming a higher new water pH); the breakdown of organic mulm or similar will lower pH while increasing nitrates. Pockets of decomposing organics are often found in areas of deep fine sand, under rocks or other décor, or in large filters (especially canister filters).



*HIGH NITRATE DANGERS:

High nitrate levels which many sources based in human studies place as low as 30- 45 ppm of nitrate as harmful. The EPA recommend levels under 10 ppm in drinking water, although often this can higher especially in well water.
High nitrate levels can cause respiration problems in fish, lower or eliminate the ability to breed, resist disease, and lower activity of aquarium inhabitants. In human studies high nitrate levels have been shown to dangerously lower blood pressure by causing the muscles that control the size of blood vessels to relax, this can be dangerous to fish too causing circulatory problems which can again result in poor disease resistance.
High Nitrate levels in aquariums will also result in high algae growths and in marine aquariums is toxic at even low levels to Cephalopods such as Octopus and to corals.

Another danger is in the bloodstream, nitrates can be converted biologically to nitrites, leading to "Brown Blood Disease".

For more on the dangers of Nitrates:
http://www.ext.vt.edu/pubs/forage/404-163/404-163.html


*REMOVAL / PREVENTION:

Here are a few basics for removal/ prevention of nitrates (I will add to this list over time too)
• Water changes; for high nitrate levels changing as much as 60% then filling the aquarium only 80% (this cuts the nitrates in half), followed by a 50% change again which will then have an over all reduction of 75%.
Also keep in mind to test your tap water as this can affect your nitrate levels as tap (& well) water often have some nitrates in the water already, I have tested as high as 25 ppm (although this is rare). So as an example you change 50% water that has 100 ppm with tap water that is 20 ppm you will not reduce nitrates by half to 50 ppm.

• Plants in Freshwater Aquariums; plants will keep lower nitrate levels. A well maintained planted aquarium maintains lower nitrates by more than one attribute:
*Direct removal of ammonia by some plants such as Hornwort (Foxtail), as well as removal of nitrates from the water column.
*The roots also remove nitrates and other nitrogenous wastes.
*Often a well maintained sand, laterite, Plant Grower Bed, etc. around the roots maintain a healthy anaerobic filter bed without reverting to sulfide reduction (Hydrogen Sulfide production), which can often happen in freshwater aquariums where sand is used if no oxygen is allowed to permeate.

• Vacuuming of eventual nitrate producing mulm is essential in both freshwater and saltwater as long as this performed correctly so as to not disturb anaerobic bacteria in saltwater or plant roots in freshwater, please see this article: “Aquarium Cleaning”

• Lower you bio load/ DOC, as noted in the previous point about vacuuming high amounts of organic mulm/sludge that in tern leads to high DOC (dissolved organic compounds) in the water column is a major contributor of high nitrates. A strong indicator of this problem is a low pH and a KH under 50 ppm along with high nitrates (often over 80 ppm).
Check your filters (especially large capacity filers such as canister or large sump filters) for buildup of mulm/sludge. Under gravel filters can be a major contributors due to trapped decomposing waste under the plates and gravel, especially not cared for well
Ornaments, decorative rocks and gravel can also trap copious of decomposing organic waste.

• Reduce feeding and use foods that are more easily digested (made with amino acids that will be used by the fish/aquatic organism and not be expelled) such as Spirulina Algae based foods.
Your choice of food and over feeding can be a major contributor to DOC and in turn high nitrates, unstable pH, and low KH.

• In marine aquariums the use of live rock, mud filters/Refugiums and/or protein skimmers can help reduce nitrates. Mud filters and Refugiums remove nitrates while Protein Skimmers remove nitrogenous wastes (proteins) before they enter the nitrogen cycle. I personally feel some older style protein skimmers can be over rated due to the often erratic upkeep they require (although the newer models are often worth the expense in both effectiveness and lack of hassles).

I prefer the more natural use of live rock (as well as live rock crumbles in filters) and mud filters/Refugiums as well as Mangrove Plants and Caulerpa algae in my marine aquariums. Good deep sand (#00) beds of over 3” (with a ½” layer of #3 crushed coral on top for ease of cleaning) also are helpful as these allow anaerobic bacteria to form and remove nitrates.


• The use of a Protein Skimmer in marine aquariums is an effective way (depending on the skimmer) of removing ‘protein’ based organics BEFORE they can enter the nitrogen cycle and thus become nitrates. These devices do NOT work in freshwater as they work via foam refraction which is a process that will not work in freshwater (there is also evidence that foam refraction will be limited by the use of carbon since carbon removes MBAS Foaming Agents, see this article: Aquarium Answers; Activated Carbon)
For Reef tanks, these devices are almost a must, and generally the low end skimmers are not adequate, high end skimmers such as Warner Marine mesh wheel skimmer or the Tropic Marine V2 Skimmer are among two of many good choices.

Please see this article for more information about Protein Skimmers: Marine Aquarium Protein Skimmers


• Use a re-circulating micron cleaning filter to super clean your aquarium without over cleaning (meaning excessive water changes over 50%). The Aquarium Cleaning Machine is an awesome device for this purpose as it removes many of the organics before they are converted via the nitrogen cycle to nitrates (similar in theory to a protein skimmer, albeit a very different process).
The key is this machine (& similar devices such as the Vortex Diatom filter, but this device is the best by far I have used) VERY efficiently removes fine organic particulates BEFORE they would otherwise go through the nitrogen cycle. Rinsing in of cartridges in CHLORINATED water after use prevents the formation of nitrifying bacteria that would break down organics resulting in higher nitrates. Despite some naysayers in some anecdotal forums, this machine is very efficient for this purpose when use correctly and it does not simply re-circulate DOC (dissolved organic compounds) through the water, it removes much of the small organic particulates before they enter the nitrogen cycle thus becoming nitrates. The theory is similar to how a protein skimmer works in marine aquariums, however this machine and similar can be used in salt OR freshwater!

Another albeit less effect device for removing organic mulm/sludge that will eventually lead to high nitrates is the Eheim Sludge Extractor Battery Gravel Vacuum. Although not as efficient as the Aquarium Cleaing Machine nor is the micron filter as effective, it still may be the answer for aquarium keepers on a more tight budget or with small aquariums where the Cleaning machine is simply not practical.


• Rinse filters often with de-chlorinated water to prevent mulm build up. This is especially important in “nitrate factory” filters such as Wet-Dry and canister filters. The rinsing of sponge filters is also important. In heavily planted freshwater aquariums this is often not necessary as the plants will often consume most extra nitrates and over cleaning can actually reduce nitrates too low for heavily planted tanks with CO2. However in marine aquariums this IS essential.
This is especially important with canister filters and Wet/Dry filters which have the reputation within the saltwater side of the aquarium keeping hobby as “nitrate factories” due to the fact that these filters both trap a lot of organic debris and also are very efficient aerobic nitrifying filters yet do little for de-nitrification. Rinsing bio media is helpful for these filters as well as increasing frequency of this procedure; this also applies to freshwater as well.


• High Porosity Bio Media: I have had success in preventing this problem with the use of live rock crumbles in place of much of the standard bio filter media in saltwater aquariums so as to allow for de-nitrification deep inside these crumbles. Volcanic rock is a substitute that works well too for this and can be used in FW as well.
As to volcanic rock and live rock crumbles, the higher the flow rate, the larger the volcanic rock/crumble size so as to allow for correct anaerobic de-nitrification (generally about a ¾ to 1 inch diameter rock size for flow rates less than 350 gph)

Another product I have used with good results (although also currently hard to obtain) is SeaChem’s Matrix. Eheim (Substrat Pro) and JBL (MicroMec) are similar products (in both cases, sintered glass) and are claiming larger specific surface areas than for Matrix, however there is a second consideration, and that is the size of the pores in the medium. Generally, with very large pore diameters, we have smaller specific surface area, so that is not good. This generally rules out pores above 10 microns in diameter. But we can go too far in the other direction as many products such as Eheim (Substrat Pro) and JBL (MicroMec) have done. If we have a very large number of very, very small pores, then our specific surface area number will be phenomenal, but the medium will not work very well as a biological medium. This is due to physical limitations, specifically too small a volume to support bacterial growth, and the decreasing efficiency of fluid transport (necessary to carry nutrients to the bacteria and waste away from the bacteria) with very small pore sizes.

As well I have also tested a product called Bio Home which has very deep pores that allows for de-nitrification (conversion of nitrates to free nitrogen); however it can be pricy and hard to obtain.

*Please note that many otherwise excellent bio media such as bio balls, bio stars, ceramic bio rings, etc., only perform nitrification, that is the conversion of ammonia and nitrites, but this only adds to nitrates as these products do NOT have the pore size and too much oxygen is available to the pores that are found on these products which oxygen in any quantity inhibits de-nitrification (the removal of nitrates)

• Macro-Porous Synthetic polymers, Ion Exchange Resins, Absorbents, etc.; there are several nitrate “sponge” or resins available, although these can be costly. Zeolite can be used in freshwater aquariums to remove ammonia before it ever goes thru the nitrogen cycle, eventually becoming nitrates.
Another popular product is SeaChem’s Purigen which can be used in both freshwater and saltwater. Purigen is specifically designed to be an organic scavenging resin. Purigen generally ignores simple elemental compounds, having an extreme affinity for nitrogenous organics
Purigen can also be regenerated with bleach, however do not use in combination with Stress Coat (for more about this please read this article: Aquarium Answers: Aquarium Water Conditioners ). Purigen can also raise your Redox, so maintain a Redox balance with the use of additional minerals such as Wonder Shells.



• Organic Nitrate Reducing Products; such as Algone for freshwater or saltwater can aid in nitrate prevention/removal.


• The use of fine micron poly filter pads inside easy to access filters such as aquarium power filters (HOB) or wet/dry filters. I would place these in easy to reach spots and NOT use them to replace the regular filters or sponges, rather place a piece in front of the existing filter. This pad needs to be rinsed every 1-3 days. How this works is this filter material will trap fine organic particles BEFORE going through the nitrogen cycle which would otherwise result in nitrates. The key is regular rinsing in CHLORINATED water so as to prevent the formation of nitrifying bacteria that would break down organics resulting in higher nitrates. This is similar to how the micron cartridges work (except on a much smaller and less efficient scale) in cleaning filters such as the Aquarium Cleaning Machines. I recommend generic versions rather than the more pricy name brands which can be cut to fit, here is one example of these generic pads: Aquarium Filter Media
The use of or micron socks, often employed in marine reef systems can achieve similar results and should be rinsed often as well for best results.


• Check your clean water source as I have tested Tap Water in excess of 20 ppm and some wells may also be high. The use of “clean water” that already has moderate amounts of nitrates lessens the effectiveness of water changes. For SW the solution is simple, I recommend the use of RO, DI or similar water for mixing all new saltwater and for topping off for evaporation. For FW, this is a bit more difficult as RO/DI water is missing VERY essential elements for fish osmoregulation so its use is not generally acceptable (the use of marine salt mix replenishes ALL necessary elements back to the water). At best the FW aquarist can uses partial RO, DI or similar and then reconstitute the water with minerals with products such as Wonder Shells, Alkaline Buffers, and Cichlid Salts.

• Carbon does not remove nitrates; although the use of carbon has its supporters and detractors, one aspect of activated carbon that is clear is that it cannot remove nitrates. Activated carbon filtration does not remove microbes, sodium, nitrates, fluoride, and hardness. HOWEVER Carbon can remove DOC, which eventually can lead to high nitrates, so the use of carbon in aquariums with nitrate problems is certainly a worthwhile endeavor.
Please reference the more in depth Aquarium Answers article about the use of carbon: Aquarium Answers; Activated Carbon

Please reference this other Aquarium answers article for more other filter media types as well:
Aquarium Filter Media; types, capacities and more

Please reference this article for more about the production of Hydrogen Sulfides during the process of De-Nitrification:
"Hydrogen Sulfide production in anaerobic De-Nitrification for Aquarium/Pond Nitrate Removal"


For a map of Nitrates in World Rivers, please click below
Nitrate Levels in Major World Rivers

For more freshwater and marine basics, please visit this Aquarium Information Resource