Calcium fluctuations

anth · Jun 21, 2019

I have recently been testing alk and cal every night using hanna checkers for both in order to set up 2 part dosing.
After testing both i adjust my alk using rs foundation and then leave it until the next night.
When i come back to test my alk normaly drops by 0.1-0.2 but my calcium has raised and i dont have a clue how.
I know this sounds crazy but i think it my be the alk im adding is causing it as it only seems to happen the day after dosing alk.

Anybody have any thoughts on this?

16/6
Alk 8.2
Cal 459
Did not adjust anything

18/6
Alk 7.7
Cal 450
Added 14ml alk to raise to 8.2

19/6
Alk 8.1
Cal 462
Did not add anything

20/6
Alk 7.9
Cal 454
Added 7ml alk to reach 8.2

21/6
Alk 8.1
Cal 455
Did not add anything an will not until i test again later

wayhighcoral · Jun 21, 2019

It appears to me that your tests all fall within the acceptable error for any of the commercially available Ca tests (yes, this includes the Hanna products). I'm suggesting that your Ca is not actually changing significantly. Even if these results were 100% accurate (not possible), fluctuations in this range of values is entirely acceptable in my opinion. Personally, if I see Ca values moving 20ish in one direction over the course of a week I might make a very small adjustment to my dosing schedule after doing my standard weekly 10% water change.

anth · Jun 21, 2019

Whilst i do agree on that i am thinking of doing a little experiment
Using hanna and salifert for alk
Hanna and marine lab for cal
I will test alk twice with both kits and cal twice with both kits
Then adjust alk and 1 hour later do the same tests same number of times.
The reason that im not putting it down to acceptable error range just yet is because when i first got the hanna cal kit i must have done atleast 5 tests in a row because it was reading 30ppm higher than the salifert kit(turned out to be a faulty salifert) and each of the 5 tests were within 1ppm of each other. Not only that but i did confirm most of my cal results with marine lab test kit.
Will post results tomorrow.

anth · Jun 22, 2019

Right
Alk 8
Cal 448 hanna 450 marine lab

Adjusted alk to 8.2 and 1 hour later tested again
Alk 8.2
Cal 482 hanna marine lab 480 (top of the chart)
Next test post will be in a few days as i am going to switch to salifert alk buffer powder to see if this has the same effect.
How can this be happening, is it even possible?
The only other thing i have been adding is lanthanum chloride which i stoped 2 weeks ago, i know this converts phosphate into a form of calcium but not in the water column and its an instant effect.

Randy Holmes-Farley · Jun 22, 2019

Calcium (and magnesium) do not bounce up and down on a daily basis. Such observations are test error, assuming the salinity is kept steady.

anth · Jun 23, 2019

I know this and is why im stumped as to why 2 different kits are reading the same large fluctuations. When i get the chance i am going to buy a third salifert kit and test with all three over the course of a few days. Im just so confused, as 30ppm is a big jump for test error especially 2 tests with 2 kits.
I did use salifert buffer powder to raise my alk to 8.4 and there was no change in calcium.