Inherited 125 gallon tank and am considering a cephalopod


Sep 20, 2010
Greetings to all,

I have recently inherited a 125 gallon aquarium and am considering a cephalopod. I am in the very INITIAL phases of my research and am VERY green to not only cephalopods but even to saltwater set ups. So I have much learning ahead to not only what species I would possibly want but to the care and maintenance of the set up. I am in no rush and want to gather as much info as I can even before I begin the process. I was hoping someone could help with

1. Ceph species recommendations for a novice.

2. A detailed list of what equipment I need for recommended species above for a 125 galloon enclosure including exact models and prices (estimates)

3. Best advice on building a custom escape proof lid for a 125 gallon tank.

4. A daily, weekly, monthly, quarterly and annual checklist of ceph care and tank maintenance.

5. All types of acceptable tank mates species specific. Meaning not just starfish - but what kind of starfish ?

6. I want to make this aquarium a beautiful show piece set up. so whatever advice about living rock, hiding spots etc in terms of beauty would also be appreciated.

Sorry I know I am asking for alot and will hopefully find out much on my own reading here but I wanted to initiate some of the info on here. I am located in Orlando and would love to visit someones set up who is local. Thanks for your time.


Staff member
Sep 4, 2006
djkaty has just started with her first tank and you may want to read through her thread as a starting place.

The marine hobby is not a cut and dried science so always read recommendations as IMO or IME:

1. No such animal. Once your tank is established, which species you start with will be more a matter of luck and availability. Fortunately, a tank of this size will house any of the most commonly available species. The exception would be a dwarf species (most commonly found are O. mercatoris) as the tank would be too large to ever see the small nocturnal animal. What we recommend for beginners is to spend time to learn how to take care of a marine environment first. Starting with a 125 has some major advantages as the water volume will be more forgiving with mishaps but leaning the basics of a nitrogen cycle and then going through the application of the concept and establishing a care routine will take many months.

For 2 and 3 set aside some reading time and go through the tank talk thread. As you will find with any marine set up, there is no ONE good answer for hardware. On the list of high recommendations somewhat specific to ceph care are the use of a sump for filtration equipment (particularly for octopuses) and a quality skimmer.

4. A ceph needs a well established tank that continuously has clean, well oxygenated water. Maintaining optimum parameters really requires picking up a good book or three on marine aquariums rather than forum posts. Different aquarist use varying timing and filtration schemes to achieve this end. One thing worth a specific mention for a new marine aquarists is the need to top off the tank with freshwater (daily or every other day depending upon evaporation rates) and to remove and replace saltwater on a scheduled basis. Some hobbiest will exchange smaller quantities of water weekly where other exchange the same accumulated volume monthly (roughly 30% is the recommended monthly total change). Water changes should include siphoning detritus from the substrate (both the sand and the rocks) while removing the water.

5. Tankmates are an often discussed and rarely agreed upon topic. There are octopus safe creatures that won't harm the animal and won't cause it to stay hidden but some of them may become dinner. I personally only keep a few soft corals and an interesting cleanup crew with my octopuses. Any brittle star EXCEPT the green ones are safe for and with an octopus. There are orange ones available that I find to be more personable than the others I have kept (two of our have names) but only when kept with an octopus (I have no idea why but the ones I have kept in non-octo tanks simply stay hidden where the ones with octos are lively and can be hand fed - often having to be shooed away from the octo food). Any serpent star, some people recommend that they be smaller than the octo but I have kept them with hatchlings without known issues. Common starfish will not bother an ocotpus but may starve over time in a tank. Thorny stars can be a brilliant orange and are diurnal and quite active. Snails of any sort (these may become snacks), small hermits (also may be eaten. I am leary of the very large common hermits after seeing one remove the leg of a brittle and then go after a second leg without eating the first but have no knowledge of one ever hurting an octopus). Hermits and snails together are sometimes problematic and the hermits may kill the snails if you mix them. Choosing snails with an operculum (attached fingernail like material that it can use as a foot and a door) gives them a better chance of surviving. Peppermint shrimp will sometimes learn to avoid an octopus (not likely a cuttlefish though) and help keep aptasia under control as well as eating waste (and nipping your hand if you hand feed any of the animals). Pencil urchins do well in an octopus tank. Others have included pin cushion urchins but I have not experimented with them. Rock or long spined urchins should NOT be included in your selection.

6. Octopuses are rough on corals and will crawl on them rather than around them if they don't sting. There are low stinging polyps, mushrooms and leathers that can generally take the abuse if well secured before an octopus is introduced and I have had good success with gogonians. Animals with a potent sting should be avoided. An octopus will learn to avoid a stinging coral but skin leisons can lead to infection and we don't have an easy way to treat them.

If you want corals to be a highlight of the tank, you might consider reading about cuttlefish. Cuttles can easily live with corals that should not be put in an octopus tank (either for the health of the coral or for concerns for the octopus' skin). As a bonus, a secure top is not required, you can keep multiples and there is a fair chance you can breed them to sustain a population.

Good live rock is excellent for esthetics, biological filtration and providing dens. More rather than less is my strong recommendation.
Sep 25, 2006
+1 to everything that D said.

The idea is to get your tank up and running, and stable, and to get yourself used to doing the regular tank maintenance chores. Keep a few hearty and inexpensive fish for a few months while you settle into a rhythm, and get the bugs worked out of your water-changing and tank cleaning methods and tools. Find ways to make it quick and easy to do water testing, water changes, tank feeding and cleaning. This way, if you make any mistakes, or discover any problems, the worst that can happen is that you lose some cheap, expendable, fish, and not an expensive, and hard to get octopus.

There's another important reason to wait a few months before you put an octopus into your tank -
Your tank will have some high-surface-area place for beneficial bacteria to grow (live rock typically serves this purpose). This colony of denitrifying bacteria is called a "biological filter" or "bio-filter" because the bacteria consume animal waste (toxic ammonia) and break it down into much less toxic nitrate. The size of the population of denitrifying bacteria living on your live rock starts out small, and increases slowly over time, eventually reaching a maximum size when it runs out of either food (animal waste) or living space (live rock surface area). Assuming that you have enough live rock (One to two pounds per gallon?) to provide ample living space for the bacteria, it will take you several months to build up a large enough population of denitrifying bacteria to consume as much waste, per week, as your octopus produces. A good way to do this would be to gradually increase the fish population in your tank until your total population of fish, is eating about as much (or more) food per week as you expect to feed your octopus. Then hold that level for a few weeks, and when the water tests show that the water chemistry has stabilized, swap out the fish (back to the fish store) and put in your octopus.
A truncated version of this process is called "cycling" your tank, but this more time consuming version will ensure that your bio filter will be able to handle the amount of waste produced by your octopus, and save the octopus from dealing with poor water quality.