Question about alkalinity.

[Art2249]

When you are tracking alkalinity, how stable is stable? I've been trying for 8.3 but it keeps moving around that number. I check around the same time each day. The only variable I can think of is when the windows are open. Does ph effect alkalinity use? Here are my numbers:
11-6 8.4 no dose
11-7 8.2 dose 22ml
11-8 8.2 dose 22 ml
11-9 8.2 dose 33ml
11-10 8.2 dose 33 ml
11-11 8.4 dose 11 ml
11-12 8.3 dose 22 ml
11-13 8.5 no dose
11-14 8.5 no dose
Also Ive been dosing 22 ml calcium each day but only check that once a week. It stays around 440. Mg 1400.

 

[Hitman]

As ph increases Alk consumption will also increase.

 

[Art2249]

As ph increases Alk consumption will also increase.

With my windows open the ph goes from 8.1 to 8.3 and when they are closed it moves from 8 to 8.2. So I guess when the weather got cold and i closed the windows I should have tapered off the alk dosing? But what is considered stable on alk? How much can it fluctuate and still be ok?

 

[Hitman]

With my windows open the ph goes from 8.1 to 8.3 and when they are closed it moves from 8 to 8.2. So I guess when the weather got cold and i closed the windows I should have tapered off the alk dosing? But what is considered stable on alk? How much can it fluctuate and still be ok?

That's kind of a loaded question as everyone has their own opinion on how stable is stable.
Personally 0.2 DKH swing is stable in my opinion and what I shoot for.
As ph fluctuations happen all day and night it's going to move, more so in the evening with lights off as ph drops and cause ALK levels would rise, then with lights on ph will rise and Alk consumption will increase again.
I once read anything 1 dkh or greater in 24 hours will stress corals out.

To help stabilize ph most run their refugium lights opposite of their display tank to minimize the ph swing as your macro will now be using the CO2.

 

[Larry L]

Your numbers are all within 0.3 of each other, I'd be surprised if whatever you are testing with can even accurately distinguish a swing that small. E.g. a reading of 8.3 on the Hanna 772 checker could actually be anywhere from 7.6 to 9.0, given the manufacturer's accuracy specs.

 

[Art2249]

Your numbers are all within 0.3 of each other, I'd be surprised if whatever you are testing with can even accurately distinguish a swing that small. E.g. a reading of 8.3 on the Hanna 772 checker could actually be anywhere from 7.6 to 9.0, given the manufacturer's accuracy specs.

I read about that too but I haven't seen it personally. I try to be consistent in how I do the test. Using a lint free cloth, putting the vial in the same direction every time. After testing the same water several times and using 2 different reagent bottles i get pretty consistent results (within .1 of each other) and even tested against salifert it is the same.

 

[Larry L]

I try to be consistent in how I do the test.

It definitely helps to be consistent, but the accuracy numbers are inherent to the device itself. Even if you do the procedure perfectly, the number on the screen may or not be the actual alkalinity, it's kind of a best guess within a range of uncertainty. Comparing to other test kits like you did, and/or using the calibration standards, is a good way gives you extra confidence that you're probably closer to the reading on the screen than you are farther away from it. I haven't seen any published numbers that talk about how repeatable the Hanna checker numbers are - mine seem to be pretty consistent if I test the same water sample more than once, but it's not unusual for it to vary plus or minus by a few tenths.