alk fluctuations

melonheadorion · Nov 8, 2023

Good morning everyone,

pretty general question that hopefully someone can answer, or have had experience with.

the usage of things like Alk, fluctuate through the day, and this is where part of the question comes in. Normally, i would expect to see high usage , no usage, high usage, no usage....
However, what i am seeing, and what i was going to try to dose for, is not as easy as it would seem, and seems a little abnormal. Currently, i am not dosing Alk, and am only dosing NP Bacto balance and calcium. Calcium is staying stable with my small doses, but as you can see below, my Alk fluctuates up and down all day. the tests from the trident are 6 hours apart, and on every 12 (12am and 12pm), the alk is at its highest point, and then drops down to its lowest point on every 6. Overall, its steadily declining, for the most part by .1~ every 24 hours, so i wouldnt have to dose much, but i was wanting to get the "wave" out of it by countering the continual drop, but when there is fluctation like this, if i dose to make up for the drop, when it reads on the 12, it will likely increase the upward trend to the 6, creating a higher swing.

Also note that the alk reading is not in the 7's. i havent calibrated in a while, but with the readings, it is about 1 whole number off, so what you see there is alk readings in the 8s (ive confirmed this with my Hanna).

I know that there will be a steady decrease through the day, if i dont dose, which seems to be happening. however, is it normal for, while in that decrease, for it to be so up and down, or is something creating an increase in Alk during its upswing? first thing that comes to mind is maybe the carbon dosing? but not sure if that would create an upswing like algae death might?

Randy Holmes-Farley · Nov 8, 2023

Those changes are pretty small, and I'm a bit skeptical of whether they are even real as opposed to some sort of artifact driven by pH changes, but there are a variety of things we do that may cause cyclic changes in alk (conversion of food into nitrate and then consumption of that nitrate) which might be a cause, as well as a slow steady dissolution of rock and sand adding alk that is superimposed on the usual depletion of alk during the day, more so than at night.

I do not know the exact formulation of bactobalance to know it it has any effect on alk. Most carbon dosing on neutral molecules 9vodka, vinegar, NOPOX, etc.) will not directly impact alk, but declining nitrate will add alk, regardless of the cause (except water changes).

melonheadorion · Nov 8, 2023

Randy Holmes-Farley said:
Those changes are pretty small, and I'm a bit skeptical of whether they are even real as opposed to some sort of artifact driven by pH changes, but there are a variety of things we do that may cause cyclic changes in alk (conversion of food into nitrate and then consumption of that nitrate) which might be a cause, as well as a slow steady dissolution of rock and sand adding alk that is superimposed on the usual depletion of alk during the day, more so than at night.

I do not know the exact formulation of bactobalance to know it it has any effect on alk. Most carbon dosing on neutral molecules 9vodka, vinegar, NOPOX, etc.) will not directly impact alk, but declining nitrate will add alk, regardless of the cause (except water changes).

i would suspect i would see a increase in Alk with decrease in nitrates, but my nitrate reduction is likely not enough to make up for the uptick, but you will know more than me. Between oct 24th and now, my nitrate has reduced 2.3. seems like such a small reduction, that i dont think it would make up for the upticks.

the part that gets me, is why would it show increases every 12 hours? if there was an uptick, i might expect to see it once in 24 hours when alk usage slows/stops, but not during a higher demand time of the day.
the changes are small, so im not worried about it, but it makes it difficult to do any dosing for, not that i need to at the moment.
as far as my ph goes, on the low end, im at 8.19 and on the high end, im at 8.3, but the fluctations on PH are the standard low in the morning, high in the afternoon. if PH was a cause, i would expect to see an inverse wave of what KH shows.
i will go with what you say. i suspect that disolution of rock is likely the main culprit. its the only thing that really makes any sense, since nitrate reduction is only happening slowly, it might have something to do with it, but probably not on this scale.

with this fluctuation, at what point in the fluctuation would you suggest to dose? at the highest point/somewhere on the downslope? im just trying to reduce the the size of the fluctuations. if i dose through the day, like i was before i found that it was doing this, the fluctuation was around a .4-.5

Jason_MrFrags · Nov 8, 2023

Testing from the Tridient? It shows an increase/decrease at those times because that's when your trident is set to test and it just makes a nice pretty graph with a curve to connect the dots.
If you tried testing alk every hour you would get a better picture of what is actually happening in your tank. .3 swing is hardly nothing in a reef tank.

melonheadorion · Nov 8, 2023

Jason_MrFrags said:
Testing from the Tridient? It shows an increase/decrease at those times because that's when your trident is set to test and it just makes a nice pretty graph with a curve to connect the dots.
If you tried testing alk every hour you would get a better picture of what is actually happening in your tank. .3 swing is hardly nothing in a reef tank.

yes, that i understand, but it still would not make up for an increase in alk during the time of day it would get used the most. even if i were to test throughout the day, its still going to show the increases like this, just in smaller intervals, but the end result still is going to be a net increase, as the graph shows.
the fluctuation isnt so much my concern, but i have to counter teh overall slow decline somehow, which is going to require dosings, so i guess the most of my concern is when during these ups and downs would it be best to dose, to mitigate higher swings.

Randy Holmes-Farley · Nov 8, 2023

lowering nitrate by 2.3 ppm will add 0.1 dKH of alk. Not quite enough to cause the uptick, but it will contribute.

The cycle is 24 h, right, not 12 h, which may mean it is pH or light driven.

That said, I would like to see actual values if, as noted, a fitted curve may be overshooting actual values.

melonheadorion · Nov 8, 2023

Randy Holmes-Farley said:
lowering nitrate by 2.3 ppm will add 0.1 dKH of alk. Not quite enough to cause the uptick, but it will contribute.

The cycle is 24 h, right, not 12 h, which may mean it is pH or light driven.

That said, I would like to see actual values if, as noted, a fitted curve may be overshooting actual values.

which values? ill give or test what i can to show them

Randy Holmes-Farley · Nov 8, 2023

melonheadorion said:
which values? ill give or test what i can to show them

Can you post the actual alk measurements and times over 24 -48 h?

melonheadorion · Nov 8, 2023

Randy Holmes-Farley said:
Can you post the actual alk measurements and times over 24 -48 h?

the one in my op is for almost 36 hours as is, or are you referring to measurements that are not from the trident?

for the sake of what it shows for longer than 24-48 hours, this graph goes back to nov 5. this is the point in time i stopped dosing alk, and it obviously started its decline, and during the non peak hours, it did what i expected it to, which was to level off before it started to drop again. no changes were made at these times, other than the alk dosing was stopped.

melonheadorion · Nov 8, 2023

to make it easier---
nov5-12am-8.59
6am-8.34
12pm-8.05
6pm-8.04
nov 6 12am-7.88
6am-7.86
12pm-7.5
6pm-7.76
nov 7 12am-7.4
6am-7.66
12pm-7.34
6pm-7.65
nov 8 12am-7.33
6am-7.57

Randy Holmes-Farley · Nov 8, 2023

melonheadorion said:
to make it easier---
nov5-12am-8.59
6am-8.34
12pm-8.05
6pm-8.04
nov 6 12am-7.88
6am-7.86
12pm-7.5
6pm-7.76
nov 7 12am-7.4
6am-7.66
12pm-7.34
6pm-7.65
nov 8 12am-7.33
6am-7.57

That's what I was looking for.

My best guesses are one or more of these three explanations:

1. Random test error that looks like a cycle, but is not. Note that at the start, alk declines for 6 measurements in a row. Then it goes up and down a couple of times. Might be random. Even flipping 500 heads in a row on a coin is an expected random event some of the time.

2.. You have a very low and steady production of alk from things like nitrate reduction and rock and sand dissolution, which normally happens but is lost under much higher demand, but when demand is very low you see it. Couple that with alk decline during the day when pH and light peak, and you get a cyclic change in alk.

3. When you drill way, way down into the nitty gritty of total alkalinity measurement, there are minor complexities that the trident is not going to be able to take into account. Specifically, then exact pH that one needs to go to to claim you have reached the actual carbonic acid endpoint varies with factors such as the total alkalinity and the total CO2 present (and salinity and temperature and how well CO2 leaves the sample during titration, etc.). At least one of these changes with pH at fixed alkalinity (CO2). Thus, the small changes you are seeing may be artifacts of changes in the amount of CO2 present.

I don't know which one or a combination of these factors it may be.

Jason_MrFrags · Nov 8, 2023

Interesting read about sort of the same issue.

What causes alk fluctuations through the day and how do I stabilize?

Why did you decide to wait a few years? Slowly built the mixed reef, most sensitive species last. If your Acro(s) is/are successful you'll have to deal with a fast growing and often aggressive coral. Every few years I grow one just for fun, but then move it on again when it gets too much to...

www.reef2reef.com

Randy Holmes-Farley · Nov 8, 2023

Jason_MrFrags said:
Interesting read about sort of the same issue.

What causes alk fluctuations through the day and how do I stabilize?

Why did you decide to wait a few years? Slowly built the mixed reef, most sensitive species last. If your Acro(s) is/are successful you'll have to deal with a fast growing and often aggressive coral. Every few years I grow one just for fun, but then move it on again when it gets too much to...

www.reef2reef.com

Thanks for posting that. The salinity change possibility mentioned there is one I had neglected here.

For the rise in alk seen here of about 7.3 dKH to 7.6 dKH to be from evaporation and lack of water replacement during that time would require 4% of the water to evaporate. High, but possible.

melonhead, what is the mechanism for water replacement for evaporation that you are using?