Mag, Cal and Alk changed so much in one day

[EthanHawaii]

Hi, I am in the middle of starting a daily dosing regiment for my 75 Gallon reef with 20 Gallon sump (all together about 75 Gallons of actual water volume), I got all my parameters from:

MAG: 1340 All tested on April 7th
CAL: 400
ALK: 7.4


to where I wanted yesterday which was:
MAG: 1460 All tested on April 7th
CAL: 430
ALK: 9.6


I waited a day and tested at the same time and I got these readings:
MAG: 1380 All tested on April 8th
CAL: 410
ALK: 8.6

I retested the Magnesium because I couldn't believe how much it went down! is this normal for this size of tank? I have a massive ball shaped frogspawn coral about the size of a 10'' dinner plate, 7'' torch coral, two 4'' Acros, a 3'' Blasto and lots of coraline on the rocks and a ball of chaeto.


Thanks,
Ethan

[ijkidd]

Ethan,
What have you dosed in between each day?

[EthanHawaii]

I dosed a mix of Magnesium Chloride and Sulfate (Reef Advantage Magnesium), Calcium Chloride and Alkalinity or Sodium Bicarbonate on April 7th until they where all at the levels I wanted.
I’m guessing I must have tested wrong the day I measured 1460 Magnesium.

[EthanHawaii]

I just tested and got this:

Mag: 1340ppm. -40 from yesterday’s test.

Cal: 410ppm. -0 from yesterday’s test

Alk: 9.6 (I raised it about 1dKH yesterday, so it’s used none today?).

I have absolutely no clue what’s going on. How can calcium go down 20ppm in one day and not at all the other? And after raising my Alk back to normal it hasn’t used any. And then my Magnesium has gone down 40ppm. I’ve read online that in even high demand tanks Magnesium won’t go down any more than 2ppm a day.

[Rondelet]

Which test kit are you using? One thing you may try doing, depending on how accurate your kit is and the resolution, is try three separate tests on three separate samples and compare the results. Better yet, try a different test kit to see how the results compare between two kits. It's quite possible that you're dealing with the vagaries of hobby test kit accuracy and consistency. I use, by most standards, fairly high end testing equipment and calibrating the equipment and getting consistent results/readings can be maddening sometimes! Also, and it's probably a minor detail, make sure your reagents are not out of date as this can and will affect the results.

Just some initial thoughts.

[EthanHawaii]

Ok, thanks, I am using non expired Salifert test kits for all 3 tests. I will test again tomorrow and if things are off again I’ll see if I can get new test kits.

[Newtious]

time frame between dosing anything and testing?

[Rondelet]

Just had a look at the Salifert Mg test kit/protocol. Keep in mind that at best, the kit as a resolution of +/- 30 ppm, which can be further out by how you read your syringe. At that recommended level 1250-1350 ppm, I don't think being out +/- 40 ppm is significant for Mg. While absolute values are important, it's much better to focus on trends once you have your parameters within the recommended ranges. When adjusting parameters via dosing, always go slow and be patient.

[EthanHawaii]

Ok, sounds good. I will boost everything up a little and wait.

[EthanHawaii]

Just wondering how much of a Magnesium swing is ok? I was thinking of maybe dosing every few weeks, but don’t know if that would be too little.

[Rondelet]

The main role of Mg in all this is to slow the precipitation of calcium out of seawater, which would affect calcium and alkalinity levels causing them to swing. It is also taken up by corals and corraline algae for structural growth. The recommended range is 1250 to 1350 ppm and is shouldn’t be raised more than 100 ppm per day. I would measure it every week for a while and then every two weeks and then every three weeks until you get a sense of how fast your system is consuming it and how much you have to add every week or couple of weeks to maintain it within the recommended range.

[EthanHawaii]

Ok, I think I will boost everything back up to normal, and start over again.