DWhatley;174412 said:
More or less, you have the idea. ... the idea is to continue to build the bioload.
I completely agree that the idea is to build the bioload. More precisely, it is to increase the size of the population of denitrifying bacteria that live on/in your live rock, and to increase it until the population is large enough to consume what your octopus, and other tank mates, will produce. You do this by gradually increasing the amount of food (animal waste (ammonia)) available for the bacteria to eat, and you do that by increasing the number of animals in the tank (bioload).
The number of bacteria in your tank will, given a little time, always rise or fall to match the total amount of ammonia (waste) produced by all the animals in your tank (your bioload). That means that if your bioload is steady for a few weeks, there will be just enough bacteria living in your tank to eat all the waste your animals produce - but no more than that. When you add another animal, the amonia level in your tank will neccessarily rise at first because there aren't quite enough bacteria to eat it all, at the new higher rate that it is being produced. Then, given a few days or weeks (depending on how large an increase in bioload it was) the bacteria population will grow to match the new higher rate of ammonia production, and things will be in balance again. During this few days or weeks, there will be elevated levels of ammonia and/or nitrite, which, if high enough, could stress the animals in the tank. Therefore it's best to start with animals that can handle these conditions without suffering (or dying), and/or with animals that only slightly increase the bioload, so that the resulting mini-cycle is so slight that it doesn't cause more than a slight increase in ammonia and nitrite.
I think that the best way to add an octopus to a cycled tank is to do it in such a way that the total bioload doesn't increase, so that the octopus won't have to suffer through elevated levels of ammonia and nitrite. The only way to do that is to remove some animals at the same time that you add an octopus. Ideally, the group of animals you remove will have been eating, in total, about as much food per week, as the octopus will eat, so that the net change in bioload will be close to zero. For this reason, in addition to the animals that D mentioned, I like to use a lot of tough, inexpensive fish to build the bioload (adding one or two fish every 10 or 20 days), and then (after everything stabilizes) swap the fish out and put the octopus in. I can sell the fish back to the LFS (usually for store credit equaling 50% of the purchase price of the fish). If my tank has only a few hermit crabs and other small animals in it, I think adding an octopus would amount to a huge increase in bioload (200% - 1000%?). If the octopus is also tiny, maybe it won't be a problem, but anything over about a 15% increase in bioload makes me nervous.
) but the idea is to continue to build the bioload. This is not really different than adding cycle fish but more productive in the end. Much of the short read literature does not explain the purpose of cycle fish and the real time it takes to mature a tank (and they don't really mature for about a year with new things developing in your LR even over 2 years - I have had sponges "show up" after 4). Most LFS want to sell you stuff so they only read the part about 0 ammonia and nitrite and don't learn about how to mature a tank.
