Have you investigated what is available in London? Here, it is not like you can order a species and have it shipped the next week. In the US we have been typically seeing Indonesian or sometimes referred to bali octopuses that are in either in the macropus (nocturnals) abdopus (mostly diurnal) complexes. These typically will do best in 45 gallons (170 liter) or larger aquarium. It appears that some of our Florida briareus are being exported and would need a 65 gallon (246 liter) by the time it is full grown. We also see the Caribbean mercatoris dwarf species (nocturnal) that can live in something as small as a well filtered, frequently water changed 15 gallon (57 liter) or even be kept in pairs.
Octopuses don't live very long so selecting your tank size should allow for numerous species over time rather than a single choice. A 55-75 tank will accomodate most we see in the US. Have a look through the tank talk forum for some ideas on configuration and hardware considerations. Use the List of our Octopuses 2008 and 2009 to link to some of the journals of different species.
Thank you for your reply, Yes over here London, The shops are very vague on what the species of octopus is. I kept one for about a year a long time ago but the system was very crude, looking back on it now poor skimmer and power heads in side the system etc, I was told by the retailer that it was a Valgaris ??????.
Now im alot older with alot more cash to play with its something i would love to do proply with the advice from you guys and girls on this site.
Mercatoris dont require much of a tank at all 20 gallon for a single or 30 for a pair would be perfect.
Tank- sealed lid, many of use just get a piece of plexiglass and cut it too fit the top.
Filter- endless options here, just remember you want one that is going to be easy to octo proof. I usually go with a filter rated for a tank alittle bigger than what I have.
protein skimmer-like filters there are alot of options and it really comes down to personal prefs
lights - some choose to have white lights during the day and red at night, i use red lights 24/7
heater/chiller- the temp depends on the species you get. Mercs are warm water so you need to be able to maintain a temp between 72-80 degrees
live rock- one pound per gallon
sand- one pound per gallon, I prefer Live sand as it aids in filtrations
water - salt