Unexpected Ca & Mg spike???

[sn4265]

My tank has been up and stable for a couple of years now. There have been no major changes or additions to the tank for a few months. I generally do about a 20% water change every 3 to 4 weeks, and I'm using vinegar saturated limewater in the ATO at about 25ml/gal on the vinegar.

My Ca had been stable at around 400-415, Mg about 1400, and Alk about 7.8. Imagine my surprise when one day last week I did the water tests and Ca was over 500 and Mg was over 1600. I asked my wife if she decided to have some fun with me and just randomly dump the jug of Tech M and Liquid Ca into the tank, but alas no. The other oddity was that pH was abnormally high at about 8.4 when it's normally around the 8.0 to 8.2 range depending on time of day.

Any ideas what might have caused a spike in both Ca and Mg? There are no obvious signs of stress in the tank. Corals, fish, inverts all are looking fine. I do have one light bulb out, but this is 1 of 8. Is it even possible for Ca and Mg to spike like this without some obvious source?

There is one other, I assume unrelated, item of note. I have been having a pretty serious issue with bubble algae lately. Lots of bubbles on the sand bed as well as on the back glass.

[downbeach]

What is your salinity, and what are you using to measure it with? Have you replaced, or opened a new bag of salt mix? Have you checked your make up water? How about a second opinion on the two tests in question?

[sn4265]

Salinity is right at 1.026 on a refractometer, and this is the same bucket of salt that I've been using, although I am getting near the bottom. Not really sure what you are suggesting I check on the make up water actually? I initially suspected the test kit, but it's obviously 2 different tests, and the Apex pH probe is also reading a couple of points higher than normal.

One other thing I thought of is that I'm using a bag of Clear FX Pro in a Phosban Reactor and it's getting close to time to change it I think. Could this stuff have absorbed Ca and Mg and for some reason be vomitting it back out? Seems unlikely, but just a thought.

[downbeach]

Salinity is right at 1.026 on a refractometer, (Is it calibrated, with a 35ppt solution?) and this is the same bucket of salt that I've been using, although I am getting near the bottom(there is some evidence that some settling of the elemental grain sizes, can occur in buckets of salt mix during shipping, which could give you a poor mixture of Ca, Mg and Alk when you mix it for WC's). Not really sure what you are suggesting I check on the make up water actually?(@ 1.026 salinity, what are your Ca, Mg and Alk reading in the water you make up for water changes?) I initially suspected the test kit, but it's obviously 2 different tests,(using the same kit?) and the Apex pH probe is also reading a couple of points higher than normal.

One other thing I thought of is that I'm using a bag of Clear FX Pro in a Phosban Reactor and it's getting close to time to change it I think. Could this stuff have absorbed Ca and Mg and for some reason be vomitting it back out? Seems unlikely, but just a thought.(Unlikely)

[sn4265]

I guess I should get some calibration fluid and double check that. I wonder if I do have a settling issue since my salt mix has always been really low on both Ca and Mg and I add Tech M and Liquid Ca to bring it up prior to a water change. I can't remember if I did this last water change or not. I'm planning on another water change this weekend so I'll double check it when I mix it up.

[bertoni]

I agree that a settling issue is a strong possibility. Do you know how long it's taken for the calcium and magnesium to rise?