Ridiculous pH swings


New member

I'm just getting my reef tank up and running and am experiencing some pretty radical pH swings that I would love to find some explanation for.

First - I've been running for about 6 weeks now w/ an aragonite (sp) sand base, and some live sand. Two weeks ago I added ~40 pounds of live rock (don't ask about the mantis shrimp). That's it.

Everything has looked fine, but, last Thursday, I got my shiny new Apex unit and placed it in the sump. For a day, the pH readings looked spot on... then they turned into a jagged mess, jumping between ~7 and ~9. Knowing that I need to be getting in the habit of water changes, I did about a 15% change. PHP immediately became a solid 8.4... until about 2:30AM last night - then, in a span of ~30 minutes, raised to 9, and then, about an hour later, to 10. It remained there will about 5:30AM, then fell like a rock to 8.2 and just been up and down all day since then.

Prior to the Apex arriving I was using a decent test kit and the pH looked ok... now that I see numbers, I'm not sure if I should be believing them, or if there's something wrong w/ my probe (or the placement of the probe).

Everything else looks fine.

A few other pieces of information -

1. The tank is a Zeroedge ~80gallon tank. Lots of aeration.
2. I installed a Geo calcium reactor this weekend, but turned it off when I started to see fluctuation. Turning it off had no effect.
3. Yes, I have a protein skimmer.
4. Topoff is RO/DI water, currently pumping through an empty GEO kalkwasser reactor.

Any ideas/explanation would be greatly appreciated. I had thought I was approaching a point where things were stable, but it appears that may not be the case. That, or my pH probe is very unhappy.

Thanks for your assistance,


Intelligent Donkey
Does the ph tester you are using compensate for temperature? you could also try running a light on your sump in reverse of your main tank aka tank on during day sump on at night. this may help a little


Appalachian Reef Society
Premium Member
You should run a reverse light cycle on your refugium, not your sump.
Sumps don't have lights.


New member
Actually, my sump has an attached refugium compartment :)

I've set the light cycle to be opposite the main tank lights... but I thought the pH was supposed to *decrease* at night, not spike like crazy?

I'm starting to wonder about the pH probe (neptune systems standard grade). I moved it to the refugium when I got home this evening, and the reading immediately stabilized at around ~8.5... no dips... no minute-to-minute swings. The refugium is fed off of the same compartment that the probe *was* in and the refugium flow is great, so... I'm at a loss.


New member
Little tiny clarification...

Little tiny clarification...

I didn't put the Apex IN the sump... just the probes :)


New member
Re: Little tiny clarification...

Re: Little tiny clarification...

<a href=showthread.php?s=&postid=15433901#post15433901 target=_blank>Originally posted</a> by growlf
I didn't put the Apex IN the sump... just the probes :)
Good piont LOL

my pinpiont will do this if it needs to be calibrated or needs a battery

how did you calibrate it