Preparing to buy octo tank


Larval Mass
Hi. I've been considering a cephalopod for over a year, but I'm just now preparing to get a tank setup and finally get one. However, I'm a little confused about just what size tank I need and what accessories to go with it. The original plan was to get a 65 gallon and a bimac, but I found a 120 gallon setup on craigslist for a good price. Is it wiser to get the larger tank regardless of what species I end up with? Also, does this ad look like it includes pretty much everything to start the nitrogen cycle?


Colossal Squid
Staff member
:welcome: to TONMO! Bigger is generally better, so if you have room, the 120 is probably a good choice. Also, it's become very hard to get bimacs these days, so you may want to consider other octos. A briareus would probably be quite happy in a 120.


Staff member
With the exception of the dwarfs, I am not sure you can oversize a tank.

As far as what else you will need to start the tank, off the top of my head I have included a list of my personal choices and here is a link to a similar discussion:

- a water source for RO/DI water. ONLY use RO/DI water or distilled water, NO filtered tap water.
- containers for a minimum of 20 gallons mixed saltwater and 20 gallons fresh RO/DI water
- more salt
- hydrometer
- test strips (for ammonia, nitrite, ph and nitrate) - you can use reagents but I have a strong preference for the stips.
- I would buy another 50 pounds of LR for both filtration and housing for an octopus.
- New sand (see my notes below). I prefer a thin (1"-1.5") sand bed that is regularly stirred there are other choices and you can use what is offered but I would rinse it well, in small quantities with saltwater and use less then the amount provided. IMO bottom substrate is just a nitrate storage unit and provides little benefit.
- a couple of 5 gallon containers to haul both fresh and saltwater for water changes
- a couple of 5 gallon buckets to use for removing saltwater
- a siphon for water removal (don't try to use one of the automotive ones, the tubing is too small, I like the ones with the squeeze bulb and wand pipe on one end)
- algae scraper metal if the tank is glass, one made for acrylic if not and extra blades (you will see a lot of algae the first year, somewhat less after the tank settles)
- gloves are helpful when handling LR to protect your hands, I have them but the cuts on my hands would show I was lieing if I said I used them much.

If you are going to buy it in parts and assuming you buy the rest, you DON'T need (and likely should not use):

4' Wood housed Metal Halide Light with (2) 175 watt bulbs, cords, ballast and fan $200 (too much for an octo tank - just use the PC's)
(1) Red Sea Prizm hang on the tank skimmer $50 (optional - there is another but if you buy the whole kit this would be a backup)
(1) hang on the tank fluidized bed sand filter $35 (optional - not a necessity but some people find they help keep the nitrates down. Again, I prefer adding LR if more filtration is needed and keeping the set up simple.
(1) Rainbow Life guard UV sterilizer housing, needs new bulb and ballast. $40 (recommendations are to avoid UV filtering with an octo but you could use it on your water storage bucket to help fight bacteria and mildew).
(1) large ModuFilter Canister and 2 pleated filters and ceramic bio core $50 (semi-optional - if you have LR, a skimmer and a sump you don't need a canister but will need something like a simple filter sock and charcoal bags where the water dumps into the sump. You will need a canister if you do not use a sump)
(1) S.O.S. Over flow skimmer to bring water to a sump 600 ~800 GPH $25 (you WILL need this if you feed the sump this way but it is far better to get the tank drilled and use gravity to feed the sump, using two pumps to exchange water is a very wet and precarious combination)
(1) 1400 GPH overflow, Acrylic, $30 - you will need this if you don't drill the tank but, again, it is better to set up a gravity fed system with holes in the tank - siphon loss is an on-going problem with external overflows. This was likely filled with the skimmer mentioned above to avoid the siphon problem but adds the issue with two pumps that cannot be finely tuned and stay finely tuned or one pump goes down while the other remains running.

Around 150 lbs. of Live Sand would be $2 a pound small quantities, larger quantities (Over 50 lbs ) $1 a pound - personal preference only, live sand is often desired but I prefer to start a tank with new sand and not with the build up in existing bottom substrates. You might want 5 pounds to put over new sand but I typically just put in new even when I am upgrading my own tanks.

Some AgroCrete hand made caves and rocks, cured and dry priced by the piece, from $5 to $15 (optional- personal preference again, I would rather see you use another 50 pounds of good live rock but sometimes the DIY rocks are very nice and, if properly created and maintained can provide similar benefits, however, this says dry priced so I am assuming it has no current biological benefit.

5 Gallon Liquid Doser, for calcium and such. $15


Larval Mass
Thanks so much for the help. It seems like, if I go with the system, the most economical option would be to buy the whole setup and sell what I don't need. It sounds as though drilling holes is the way to go, I imagine it also cuts down on the overall noise level. Do you have any experience with


Staff member
We are total chickens when it comes to drilling a large tank so we took our very old 65 gallon tank to our not so local LFS and had them drill it for us for under $50. You might investigate this option first unless you are comfortable (many say it is easy but this particular tank had some unusual oddities and we wanted someone with lots of experience to attempt it - and it was a total success). It was a pain taking it there and picking it up but I would do it again in a heart beat (at twice the weight, DIY might be the best way though since you do not have the oddities this tank included). No one will guarantee the results so don't make that part of your decision but do look for someone who frequently builds out salt tanks if you have someone else drill it for you. Check more in the tank talk thread as I remember several discussions on drilling and keeping the surface lubricated ( but you can use the advanced search and look for drilling in the title for more). To be honest, I don't know of anyone that drilled a non-tempered tank that cracked their glass (I even know of a person that did not crack a tempered tank until the second hole :roll:)


Haliphron Atlanticus
Maybe used tank prices in your area are higher than mine, but those prices seem way too high to me. I suggest that you wait for a better deal, or at least learn what normal prices in your area are. Big tanks are harder for people to sell, especially during economic hard times, so you should be able to find someone who is very eager to get rid of a big tank, and will take a low offer.

Only buy a used tank if the owner can convince you that no copper based medication was ever used in it. Copper contamination kills octoupses, and you can't clean it out.

You might want to consider ordering a new tank from They can build you a 90 gallon (48 x 18 x 25) for $207 plus a fee for custom overflow, holes drilled, etc. Their stands are nice too. Used is still probably a much better deal if you can find what you want, but if not, consider them. I love the tank I got from them, despite the surly customer service.

Members online

No members online now.