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Weird octopus and some water issues....


Jun 15, 2021
Aurora, CO
Hi all, even though this is my first post, I've been a member here for about 6 months and have found so much helpful information here. I've had 3 octos over the past few years and recently brought my newest home. He is by far the most bizarre creature I've housed. For starters, what was marketed as an Atlantic Pygmy Octopus is THE LARGEST Pygmy octopus I have come across. He was shipped with a little piece of PVC pipe and tried to stuff his humongous body in that little pipe and was spilling out of both ends!
So I'm not quite convinced he's any sort of a dwarf octopus because he is just huge and he eats almost a much as my full grown Abdopus use to!

He acclimated just fine, and a little while after I released him into my aquarium he began to dig. Everywhere. I have all of these little mounds of sand all over my tank! That would be fine except now the water quality is all over the place. My tank is about 14 months old, it's a 32 gallon; the water parameters are generally Nit/Amm 0, Nitrate 0-5, sg 1.026 and the pH has always, ALWAYS been 8.0-8.2. I will be the first to admit that I don't go crazy vacuuming my sanded- I did that once a few years ago and killed all my fish with a huge nitrite and ammonia spike afterwords so I just lightly clean off what is on top now and leave it alone. Shortly after he began his construction projects he nitrite went up to .5 so did the ammonia; I did a couple water changes and that has since normalized. Now my pH is suddenly 7.4! I don't know what to do, the octopus seems to be doing fine, he is eating ok, currently wedged under a rock and throws things at me when I go check on him so I don't think he's too bad off.

Has anyone had an octopus tear up their tank like this? Also, what should I do about the pH, daily water changes or do I need to get some sort of additive? I've never added anything in this aquarium, it's been stable once it finished cycling. Do I need to try to get him out of there until the pH comes up? I've left him alone because he doesn't seem to be stressed or struggling in anyway- I kind of thought trying to get him out would be more stressful than the pH dropping to where it's at. I'm including the best picture I could get of him, and it's not that good because there's some algae on the glass that I had been trying to remove previously. And he wasn't too thrilled about his impromptu photo shoot either. If anyone has any info on what type he could be I'd welcome any input. I will try to get a better picture if the opportunity presents itself.

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Some other things I want to add. How big would you say it is? Judging from the eye papillae I am thinking mercatoris.
Also you aught to does some baking soda to get the ph up if it has not returned to normal already. For your sized tank does 1 teaspoon of 100% baking soda( aka sodium bicarbonate) every 24 hours until it has returned to normal and if your ph is not stabilizing after some time I would add some crushed coral substrate to your filtration.
If this octopus does turn out to be a larger species I wouldn't worry to much. Just make sure you have a protein skimmer. Octopus can go in smaller aquariums than people think. What kind of filtration do you have going? If it does get larger I recommend more activity. More things to stimulate it.
I would leave the octopus in the tank for the time being. pH of 7.4 is okay for short periods of time but try and get it back to 8 if possible. 1 teaspoon of sodium bicarb per day seems right to me as well. You could dissolve it in 2-5 cups tank water and use a drip line to add it back to your sump to prevent swinging the pH.

Undisturbed sand is notorious for harboring all kinds of nasties. I would recommend mixing your sand every week or so, or do a more thorough job of siphoning it while doing water changes, otherwise your problem will continue. You could also get crabs or snails or something that will dig around in the sand on their own, but they will be more difficult to keep alive with an octopus in the tank.

Be careful not to turn over all your sand at once, especially if your tank has a track record of having problematic sand. You can probably clean small sections of your tank every day until your issue has been resolved.

Have you tested the pH on the water you are using for water changes? You may have to dose sodium bicarb in your water changes in order to keep the pH up as well.
I am going to go the opposite and tell you to simply aerate your aquarium to raise pH if you are worried about it. Dosing can cause Alkalinity to swing wildly and I have had many encounters with people trying to raise pH and ending up with their Alkalinity at 18 or higher (shoot for roughly 8.5-9 for Alk). A big Alk swing can kill a lot of things in your tank including your octopus.
So I actually ended up moving her (I’m pretty sure it’s a her now that I’ve seen her more) over to my 20 gallon cube that I usually keep live food in because the pH dropped some more, the ammonia started coming back up and she just wasn’t looking very good (and she’s pretty much destroyed the bottom of that tank). So glad I did because she is worlds better now and is coming out for short spurts around dawn and dusk. I was able to get a few pictures this morning and I think she is a mercatoris. She’s is about 3” I’d say from mantle to the tip of her arms.

She’s funny too, the last couple of mornings she’s been coming out of her den and over towards where I’m sitting at my desk and throws her “trash” at me and then runs back to her den to barricade herself in for the day!

Not a single hole dug in this new tank so now I’ve got to figure out what is wrong in the other one that she dug all those holes and then try to stabilize the water again. There’s nothing in it right now so I may just give the sand a thorough cleaning and then just let it sit and stabilize for a while.


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That sounds like mercatoris behavior- throwing things at you. 🤣. Looking at that picture, I’d agree with that ID.

Sounds like you’ve got things under control! I think she’ll be happier in the smaller tank, and you’ll have more interaction. Good call!
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