LOL, the purpose for our keepers' journals is to ask, answer and share so no questions need apologies.
Live rock and cycling saltwater tanks is not a defined science but often a pet store has no real clue about the condition of the LR or what advice to give on cycling (the exceptions are usually owners and employees who keep saltwater at home. Most live rock I have seen in pet stores is kept in a tank without animals. Detritus from the animals creates the ammonia that feeds the bacteria. When the rock is initially harvested, it will contain critters that will die off and make ammonia, however, over time there is no more food for the bacteria and it also dies. It is a difficult balance for the store keeper because he/she can't put new LR in with saleable fish but can afford the room to keep the rock cycled.
When you take your water into a pet store to see if your tank is cycled, almost never do they ask if you have seen a ammonia and nitrite spikes. What results is people putting dead rock in their tanks, letting it sit for a month and then getting the OK to add critters because there is no ammonia or nitrite in the water. Unfortunately, there is often no bacteria either and the infamous, New Tank Syndrome occurs. If you Google New Tank Syndrome you will see tons of articles. Here is one of the first I noticed
Enter an octopus. Octopuses are very messy eaters and produce more ammonia than a large fish. So even if you have actively (ie continually added ammonia producing cyclers) cycled your tank, observed an ammonia spike, a nitrite spike and then see them go to zero (usually about 1 month), you still need to continually build the bacteria to take the waste load of a large animal. This is why I try to stress the word active
when talking about a 3 month minimum cycle.
So, what to do. Watch for heavy breathing. If you see it, change water ASAP. If you don't have a way to test your own water, invest in either reagents and/or test strips. I have come to rely on test strips because they are so easy and take only a few seconds but others frown on them (they are invaluable for acclimation). They do need to be fresh and kept completely away from moisture. Keep an eye out for ANY ammonia or nitrites (I suspect you may only see the later at this point). Over time your live rock will grow more bacteria. You can add more live rock but do take the precautions I mentioned by keeping it in a separate container with moving water for a week (or until you see no ammonia or nitrites whichever is longer) before adding it to the display. In an emergency, the chemical neutralizers have been helpful (do not add them to your new LR bucket!). I tend to shy away from them but none of my tanks are less than 5 years old or over crowded so I have not had to worry about ammonia for a long time. @sirreal
recently faced an issue and adding a neutralizer may have saved his animal.