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 . 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.
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
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).
OK, thanks. I have enough LR to make plenty of hiding places and undercover spots.
Would it be fair to say 120 watt will be sufficient for mushrooms to nourish if high in the tank? If so, going to buy a cheap one and see how it does...if it survives the decorator crab, sea urchin and star fish. Although the sea urchin doesn't move so don't see him as a threat...
I'm really looking forward to seeing strange new growths in my aquarium...aware it can be a pain eventually (probably), but can't wait to see it happen.
You might get away with a single 60 watt power compact if you keep the soft corals under the light (there is no rule that says the entire tank must have the same lighting). I have not looked at fixtures for awhile so I don't know if you would find a two bulb unit that spans the tank. I think aquariums and cheap are likely to be Oxymorons
LOL, I was waiting for CG to say something about your intelligence statement. There are a number of people who feel cuttles have the upper hand in the brain category. I refrain from forming an opinion until my brood age a bit more .