Can anyone explain this?

A couple of questions.

0 dKh?????? Is that a typo? If not, then there is something wrong with your test kits. 0 dKh seems impossible to me in any manner unless you purposefully removed it. Check your testing vials and kits for something that may have got into them and contaminated them. That seems to be the most logical thing here. I would buy a new kit and test it with that and keep it completely separate from any other potential contaminates.

Have you accidentally mixed the titration chemicals or used lids on the wrong bottles? Just using the same lids may leave enough residue from another test kit to throw things off.

Hmmmmm... I still think I has to be something with your test kits. I can't see any possible way to have such low dKh and still have any life in your tank. Your pH would be so acidic you corals would have had skeletons dissolving.

What time of day did you test it? Your ph will fluctuate throughout the day, make sure you test it at the same time of day. Best time is just as your lights go off, it will be at its highest.

One thing I noticed just now is when your mag and calcium are really high, you seem to read very low alk. try a test on some test water where you have a few different levels of mag and calc and see what the alk is between them.

Another thought, are you using a dosing system or doing it by hand? How long after you dose are you testing?

I'll get a pic of the tank up this afternoon.

I don't have a refugium because it's an RSM 250.

This is in my front room which has three west facing windows. The tank gets about 4 hours of sunlight in the summer and around 2 hours in winter.

The sand is CaribSea Arag-Alive Special Grade reef sand. There's somewhere around 70lbs in there now. It's about 1.5"-2" deep if smoothed out. Thanks to an MP40 the sand tends to shift to one side.

The alk has always been stable in the past even without a calcium reactor. It had a consistent trend of decreasing or increasing rather than an up-and-down unstable pattern. Calcium and magnesium aren't really a concern, I just don't like my calcium to be above 475. I prefer to keep it at 450.

I really don't believe the 0 was correct, but as I said early, I tested it 4 times with 2 different kits that have never had problems in the past. When I have the calcium reactor running I always tune it to maintain alkalinity before calcium. It tends to keep everything (calcium, alkalinity, magnesium, ph) more stable in my tank if I set it this way to begin with.

Normally I wouldn't worry about a low ph reading if everything was doing well and I'd not seen any adverse effects, but I don't want to turn the co2 back on in my calcium reactor if the tank ph is already low. I'm somewhat worried it would bring my ph even lower in the display. I've always had a hard time keeping the ph above 8.1. I've checked it in the mornings, afternoons, and evening over the last little while and it's consistently between 7.7 and 7.8 every time I check it.

Ph is measured with the ph meter which was calibrated a week ago. The probe is in a port on the top of my calcium reactor. I do not have the co2 turned on and there is not a valve restricting flow to or from the reactor right now. I'm pretty sure the ph in the reactor is the same as in the tank because I've also used an API liquid test which matches the probe in the reactor when testing water from the display.

Edited by Ann_A - November 03 2013 at 1:56pm

All of my levels are stable now. My only concern is that my ph is now sitting at 7.5 all day every day. At 5:30 this morning it was 7.5 with the ph controller and the liquid test kit. Last night at 7:30 it was 7.5 with both the controller and liquid test kit. I've tried throwing an airstone in the tank for a day and a half and that didn't do anything. I've left the hood open with the airstone in the tank, opened the skimmer valve all the way (removed the collection cup so it wouldn't over skim) and that didn't help. My best guess is that the CO2 levels in my house are high enough to keep the tank's ph down. Anyone else think this is a possibility? I tested the theory by taking a cup of tank water and leaving an airstone in it overnight and checked the ph. It didn't change. And if this is the case how can I go about fixing it without opening doors and windows all of the time or running fans all over the house? Should I add a CO2 scrubber to the skimmer's air intake?

I'd have to run it about 15ft even if I ran it straight across the room... that's really not an option.

The furnace is on the other side of the house in the basement. I don't think my parents would go for running tubing all over the house either.

Anyways, I took another cup of tank water and put an airstone in it, but this time the air pump and cup were set outside. Ph came up to 8.3 so I think the problem is an accumulation of carbon dioxide in the house.