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Introducing fish to cycled tank before octopus...


Dec 13, 2013
New York City
My tank has finished it's cycle over a while ago, and the last week I've had some critters in there.

My tank is a 55 gallon. Salinity stays at about 1.025. Tank inhabitants at the moment:
  • 2 pepperment shrimp
  • 1 fire shrimp
  • 1 decorator crab
  • 1 sea hare
  • 1 red knobby star
  • 2 turbo snails
  • 2 margarita snails
  • 5 red leg hermit crabs
  • 2 emerald crabs
  • 3 bumblee snails
I also have some macro algae in the tank.

I don't mind if the Octopus eats anything I currently have when I get it, and will remove the decorator crab as a potential threat.

I've been advised this isn't by any means a sufficient bioload to maintain my bacteria population.

I've been advised to add fish, but wanted to avoid this for two reasons: 1) To avoid any possibility of introducing copper in to my tank and 2) because I know they are hard to remove.

I would like to know if there are any fish that I could add that would be fine with my setup at the moment, are unlikely to be treated with copper and can be easy to remove.

Other suggestions in place of fish would also be welcome. I was planning to add a red brittle star, but haven't managed to find one in a LFS yet.
I agree with you and your reasons for not adding fish and don't cycle my tanks with them, however,
My tank has finished it's cycle over a while ago
is not overly helpful to know how long you finished your initial cycle and what you have been feeding it after the initial 0 ammonia and 0 nitrite occurance. We recommend at least three months of heavy feeding after the initial cycle to build up the bacteria to handle the heavy load of an octopus. Feeding your clean-up crew chopped up table shrimp now will help build your bacteria without needing to add fish. You will want to perform regular substrate cleaning to minimize the nitrate build up.

A critical question is, "how much live rock do you have in the tank?". Your live rock will contain most of your denitifying bacteria.

Your new cleanup crew is a good start. Yes the octopus may eat everything but the knobby (one of my favorites and does well with an octopus). I successfully keep red legs with my octos but there is no guarantee the hermits won't be eaten. On introduction, an octopus often eats/kills anything that moves but tends to be content with leaving snails alone after it learns it will be fed easier food regularly (the one exception I have had was O. vulgaris - LittleBit ate anything that moved, except the starfish/serpent stars). Any crabs are food (mithrax and decorator). The peppermint shrimp may or may not survive as they seem to be quick to learn to avoid being near the octopus but sometimes it takes one being eaten to understand. What kind of seahare? If it is the larger variety, it may ink the tank when molested and probably should be removed. If it is a lettuce slug, it is supper.

You might also add a serpent/brittle star (I am particularly fond of keeping the red, Ophiocoma wendti ). These are excellent scavengers and will often train to be hand fed if desired. They do a very good job finding even relatively large chunks of food and will allow you to overfeed the tank. We keep one in each octopus tank and name them all Pesky. They often share the octopus den (and locating them is the first thing I do if I can't find the octopus) but will also try to take offered food (hence the name). The octopus would have no trouble taking the food away from the brittle though and they are a bit of color for the tank. Other serpents/brittles are fine as well but avoid the green as they get aggressive as they get large and may trap a small octopus. There has been some anecdotal evidence that the Bahama star may also post a threat and is off my safe list.
During my cycle I added enough ammonia to count for a heavy bioload, getting it to the point I can add ammonia to 4ppm and have 0 ammonia and 0 nitrites in 12 hours.

My concern is that the current inhabitants are not sufficient to sustain the bacterial population I built up while cycling.

I have about 65 pounds of LR in my DT and I would estimate another 20 in one of my sumps Also about 40 pounds of LS in the DT.

I've done my research and understand the best way was to add a CUC, then a brittle star then eventually the octopus. I'm still looking at adding a brittle star but have yet to find one.

However, a red brittle star is still going to be reclusive and not overly acting during daylight hours, at least from what I've read?

I'd like to add something that I can see doing stuff during daylight hours, that will hopefully not get eaten by the octopus (although I don't mind if this happens), or that I can remove easily later on. That's why I am wondering if there are any fish I can introduce and easily remove later on without fear of introducing copper to my tank.

If there isn't, then is a brittle star really sufficient to sustain the bacterial population needed for an octopus?

My sea hare is the larger variety and does have the possibility of inking. Is there a danger to the octo with this? I will make sure to remove it before introducing an octo if that is the case.

In the event I add only a brittle star, will it get along well with the fire shrimp and decorator crab if well fed?

I understand both of those may be food for the octo, but would rather not lose them to a star if possible.
Some starfish will capture even fish but the shrimp are far too fast for the brittles and most serpents. I have never had a brittle/serpent star both live animals (with the exception of the green serpent star). Crabs may nip at the brittles arms but not to an extent that there is permanent harm (I see mine missing tips frequently and there is nothing in the tank to remove them - the arms continue to grow). Fire shrimp are an odd choice for food and I would see if your LSF will take it back in exchange rather than leave it in the tank for the octopus to eat.

My personal rule of thumb is, NO FISH in an octopus tank.
The fire shrimp was on sale at Petco, and they won't take it back.

Of course I would hope it would not end up as food, but won't be heartbroken if it does. As long as it isn't a danger I will let it stay.

I will remove the sea slug before putting in the octo...ugly thing it is anyway.

So the brittle star won't be active during the day, and it sounds like there really isn't much I can add that would be active during the day to look at, unless I'm lucky and the brittle comes out to play.

I should note I also have a pencil urchin, which I read to be octo-safe. Damn thing seems alive enough but never, ever movies when I'm watching, and never moves much...

I've read the red knobby star and decorator crab are not reef safe and may not do well with corals. If they do I would love to add some mushrooms and gorgonians.

DWhatley, I know you have experience with keeping corals and an octo together. My current light is soft, only 17W. Would this be sufficient for leather corals and mushrooms, or is it too soft for any coral?
After I've had the brittle for a few months and my tank is mature, would it be fine to introduce an octopus?

I will have:
  • A protein skimmer rated for 3 times my DT size
  • A mature bio filter
  • 60lbs LR in a 55 gallon tank, more in sump
  • No dangerous tankmates
  • A well rounded CUC
  • A decent pod population
  • Soft light and a red light for night viewing
  • Chemical filters...Purigen instead of carbon, as well as PhosGuard and CupriSorb
  • An ATO system
  • An octoproofed tank and equipment consisting in part of enkamat, velcro, mesh bags and astroturf
  • Filter sponges over return pump intake to prevent bubbles in DT
  • 15% water changes every week
  • A supply of live food, thinking either fiddler crabs or ghost shrimp
  • Refugium with macro algae
  • Shaving brush, Halimeda, Sea pansy in main tank.
  • Octo safe toys..clear plastic pipes, legos, safe balls, a clay flower pot perhaps..
  • At least 6 months experience in doing water changes, monitoring levels and doing tests, feeding and general maintenance..
Octopus will be drip acclimated following posts on here and instructions in the the book from Nancy and Collin.

Have I missed anything?
Other than the chemicals (I am a proponent of carbon only. The ones you are using should be fine but I would add carbon, Phosoguard is for phosphates and CupriSorb for metals - which you should not have, Carbon removes more waste and will keep your water clearer) and making sure you over feed the tank while you cycle you appear to be on your way.

I keep only a very few corals with the octos. I have found one set of polyps that the octos will touch without retracting their arms and I have propogated them in the other octo tanks. I don't have a proper name for them and all others I have tried I have removed because the octo reacted. You can try mushrooms, gorgonians (there are a few not so pretty species that are not photosynthetic) and leathers high in the tank (as much in the water flow and out of a guessed octo path as possible) to see how they do but only buy ONE for the test (you can add more if it survives and you like it). I would mount anything that you try on its own, movable rock to be able to change its place it it does not appear to feed (open up).

When you read that something is not "reef safe" it means it may eat corals and is not necessarily a problem for the octopus. If thornys are well fed, they should ignore anything you put in an octopus tank (but not in a reef tank). The pencil is fine but they do tend to chew on most anything. As you noted they are slow moving. One of mine will occasionally mess with a gorgonian in its tank but I simply (sometimes not quite so simple) separate the two and move the urchin.

The toys are not likely going to be of much interest so don't invest a ton but you can experiment without harm.

You may find you want a more active environment that what a species tank usually provides. After you keep an octopus, if you feel the tank is too "dead", you can convert it to a fish tank as is or go a step further to a full reef (your lighting would need to change). Alternately, if you really enjoy the octopus but still yearn for activity, you can join those of us with MTS (Multi-Tank Syndrome) :sagrin: and experiment with a nano or larger tank to add activity to your displays.
I had Cuprisorb as a precaution after my tank was initially filled with tap water. I'm thinking Phosguard can't hurt. I'm opting for Purigen instead of carbon. I know opinions are divided on this, but having read carbon can be a nitrate factory, I'm opting to try what seems to be a more efficient method. Purigen will still take ink and such out of the water if the need arrises. Can always switch to carbon later if I need to.

I'm not sure why you say to overfeed while I cycle...my cycle has completed? Everything I've read indicates the cycle is complete when you can can add ammonia and ammonia and nitrites are 0 about 12 hours after adding. Only reason I'm not adding the octo yet is because I want the tank to mature...get more algae (not too much), get a pod population, a stable CUC etc.

I thought the toys were a key aspect of owning an octopus, as I need to ensure the octopus is stimulated? I thought toys were the key to doing that, in part, as well as "feeding puzzles" such as putting a crab in a childproof medicine container (washed thoroughly of course). I guess I'll see what it does when I finally get it.

When you say I can convert to a fish tank as is, that would meen getting rid of the octopus, right? Not something I will be doing in the next few years, even if I replace it due to short life span.

I think looking at adding "safe tankmates" from the various lists and such should add a bit to the activity. Besides, I still have to investigate species and see which one is best suited to my setup. I know at least one of them (from reading the box of chocolates post) can be active during the day somewhat.

Is a 17W lamp sufficient for leathers, gorgonians and mushrooms, even if high in the tank?

Thanks :smile:
You would not be able to remove the mantis shrimp (at least not without disassembling your tank) so no, not a good idea. Mantis, like cephs, need a species only tank.

You won't be able to keep photosynthetic animals with 17 watts but you can look for some of the non-photosynthetic gorgonians and sponges (these are hard to keep alive but several require low light).

Yes, if you add fish, you would not keep an octopus. Understanding that you want to see movement would suggest that A. aculeatus is going to be your best bet for species but heed the warnings about what you order vs what you might get. Toys are usually ignored by the smaller animals but even with the GPO's (Giant Pacific - far too large for a home tank), keepers remove the toys after a short time. The news media tends to hype the toy part of stimulation but live food, and things it can safely watch (several observations suggest keeping a fish tank within view may keep them entertained without harm but it is not fully understood if this is because they fear predation or satisfies curiosity. I am in the later camp and my octos see each other as well as a fish or two - at a distance) are closer to reality. In his memories of long time cephalopod specials, Roland Anderson, @gjbarord mentioned that Roland half jokingly suggested that perhaps putting a large predator in the tank would be the ultimate enrichment :biggrin2:. Keeping a nano with fish might serve to satisfy your desire to see ocean movement, keep a few corals AND provide enrichment.

One other alternate you might consider, now or in the future, is keeping cuttlefish. These are also personalitied cephalopods but the S. bandensis tend to swim/hover rather than crawl into a den. They have many of the color and skin changing attributes of an octopus but are more visible and move about more often. The biggest drawback is the cost of feeding them.

Your tank has reached the initial cycle but cycling is an on-going process of building bacteria (not stabization) to handle waste products. If you were building out a fish tank, your tank would be ready for a small number of hearty fish that would eat food, poop and continue to grow the bacteria that will convert ammonia to nitrite and nitrite to nitrate. Overfeeding your cleanup crew does the same thing. An octopus is the equivalent of a very large fish or a tank full of smaller ones so a newly cycled tank does not have enough denitrifying bacteria to handle its waste. Growing algae has no benifit.
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Thanks Cuttlegirl. I'm away from NYC so much these days for work though, don't know when I'd have time to join up or be an active member.

Thanks for all the explanation DWhatley. Despite my research, there are not many available answers due to this being such a niche hobby, so it's great to have someone fill in the blanks, no doubt helpful to other people also :smile:

I didn't know the mantis shrimp was hard to remove. I'm still looking into it as there seem to be a bunch of species. Biggest problem is I don't think I would have anyone to give it to when I was ready to get the octopus. I can always try one after the octopus.

Thanks for the notes about toys. I won't over do it and won't rely on toys to keep the octopus stimulated...will always try new things and see what works and what doesn't.

I haven't really considered cuttlefish yet, as they don't seem to be anywhere near as intelligent as an octopus, which is my primary interest and fascination with these animals.

Are there non photo-syntehtic mushrooms as well? I tried searching but everything I found said all coral mushrooms are photosynthetic. If that's the case, is a brighter light OK during the day, or is there another solution?
A brighter light is OK during the day but be sure you have plenty of very dark den areas. I would avoid halides (some members have used them with cuttlefish but I suspect octopuses are more light sensitive). Compact PC's are fine. I just replaced a 120 watt (actual fixture was 240 but I was only using 2 of the 4 bulbs) power compact fixture with LEDs but will have to wait a month or more to report how well the mushrooms, polyps and gorgonian survive under the new lighting (the new lights should be roughly equivalent to 90 watts fluorescent). I have a different brand of LED over my lobster's tank and the single leather does well high in the water column. Interestingly, I have new growth that is either a cluster of mushrooms or a very interesting macro algae (I suspect the mushrooms) that has magically appeared low in this tank. These are a nice burgundy color and I have no idea where they came from (not all that unusual but oddities showing up in an older tank are most often sponges).

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