• Looking to buy a cephalopod? Check out Tomh's Cephs Forum, and this post in particular shares important info about our policies as it relates to responsible ceph-keeping.

Alkalinity Levels


Mar 14, 2006
Over the weekend my gf and I were able to acquire a mercatoris (we think). We currently have her in a 5.5gal tank (we're still in the process of octo-proofing our 50gal tank).

We named her Ossie. She's quite small I think her legs are about 2-3 inches and her head 1.5" - 2". We are feeding her ghost shrimp, and hermit crabs, and oh boy is she eating!

When we first put her in the tank, she gobbled two ghost shrimp and one crab. I didn't see her much on Sunday (she has found a "comfy" den in on of the living rocks), but I stayed up last night with a mock infra-red flashlight, and was able to witness her hunting. We had just put four snails in the tank to help with cleaning, and we're assuming she ate one, as we have only been able to find three. Last night she ate one crab, it was so cute, she carried it back to her rock, and tried very hard to get it, shell and all, to squeeze into the hole that she migrates through.

She came out about 3-5mins after we had turned out the lights, and didn't seem bothered by my flashlight. I tried to get a picture of her, but not wanting to startle her I didn't turn the flash on, and was unable to capture her on film due to the lack of light. I hope to get a shot of her one of these days.

Anyway, to get to my reason for posting. We have been reading up on the care of octo's and have learned quite a bit. For one we need to hurry up with getting our 50 gal ready, and get her some toys so that she will be able to tease her brain.

We've been testing the water every day, some times twice a day and are planning on doing a water change this upcoming weekend, if not sooner. The results of our testing have been relatively the same:

temp.: 70-75 degrees fahrenheit
saltinity: normal (I can't remember what the number was)
ph: 8.0
alkalinity: normal

I was concerned about our ph being on the low end, as I've been reading optimum is 8.4, so we tried using a buffer, which raised the ph to 8.4 and the alkalinity to high. Eight hours later we tested it again, and the ph was back to 8.0, but the alkalinity was still at high. I don't want to use the buffer again, because I'm afraid of what the high alkalinity means. Hence why I'm posting, how can we get the ph up, and the alkalinity down to normal again?

Ossie seems to be all right, as I said last night was the first night I really got to see her. We have hermit crabs in the tank with her and they seem to be thriving, though dwindling in numbers, yet thriving just the same. She is eating, one average (at least what I witness) she's eating about 2 ghost shrimp (these we provide at the same time every day) and one crab. I have to admit that when we wake up there is a dramatic decrease in the activity in the tank, which I'm attributing to Ossie's late night hunting.
umm 5.5 gal tank is amazingly small
the water quality shifts in a tank that size are traumatic and extreme
get that 50 up ASAP.
there is no way a 5.5gal is going to be able to handle the protein generated by an Octo.
dont mess with water too much until you move her. no sense in spikeing the water one way then another.
what is the problem with the 50?
My PH is generally between 8.0 and 8.4
depending on what Zim didnt eat and I havent found yet
ph at 8.0 should be fine for the short term
dont know about the alk.
I wouldn't be too worried about the pH or the alkalinity. Especially in a system that small.

One octo-proofing tip for young octos is to put them in a plastic "Critter Cage" that has a bunch of tiny holes drilled in the side. If you've got some sand and dens and toys in there the octo will be plenty happy, and you won't have to worry about never seeing them again in a giant tank. When it gets a little bigger you can just open the lid and he'll find his way out.

Hi Akyu,

As you may know, saltwater chemistry is pretty complex with everything affecting everything else. One of the things that affects pH is the ratio of O2 to CO2 and it could be that you just don't have sufficient gas exchange to maintain an optimum level of O2 in such a small tank.

I'm guessing that your pH problem will be solved when you move Ossie to the larger tank. In the meantime, you might want to increase your water circulation such that water is constantly being moved to and across the surface of the tank. It could be as simple as re-aiming your powerheads.

The permanent solution, as others have already said, is moving Ossie to the big tank as soon as possible!

Breathily yours,

Sponsor Banner
please support our sponsor
advertise on TONMO

Shop Amazon

Shop Amazon
Shop Amazon; support TONMO!
Shop Amazon
We are a participant in the Amazon Services LLC Associates Program, an affiliate program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.