Daily alk swing. What's the cause?

[ReefDreamz]

Main question: What is causing my alk to be higher at 6pm compared to 12am and 12pm?
Details: My Trident measures alk 4 times a day, 12am, 6am, 12pm, 6pm. At 6am and 6pm the alk is always higher than at 12am and 12pm. To maintain alk I'm dosing saturated kalk between 7pm and 7am so I understand why the 6am test measures high alk but why does the 6pm test also measure high alk when the kalk has been off for 11 hours before that? Similarly, why is alk lower at 12am than 6pm when kalk has been on for 5 hours prior to 12am?


All the peaks here are at 6am and 6pm, all the valleys are at 12am and 12pm.

 

[Charlie the Reefer]

Main question: What is causing my alk to be higher at 6pm compared to 12am and 12pm?
Details: My Trident measures alk 4 times a day, 12am, 6am, 12pm, 6pm. At 6am and 6pm the alk is always higher than at 12am and 12pm. To maintain alk I'm dosing saturated kalk between 7pm and 7am so I understand why the 6am test measures high alk but why does the 6pm test also measure high alk when the kalk has been off for 11 hours before that? Similarly, why is alk lower at 12am than 6pm when kalk has been on for 5 hours prior to 12am?


All the peaks here are at 6am and 6pm, all the valleys are at 12am and 12pm.
View attachment 2996525

idk if this can help you / is the culprit

but, what does your return pump chamber / ATO setup look like? Wondering if salinity fluctuation due to top off routine is a cause.

I’m also very curious to see other responses

 

[chipmunkofdoom2]

The real issue is the asinine scale that Apex uses for this graph. It only looks like your alk is swinging because the y-axis goes from 8.3 to 8.8. If you adjust the scale to 7 - 11, what reefers usually target, the "swing" looks miniscule:

 

[ReefDreamz]

The real issue is the asinine scale that Apex uses for this graph. It only looks like your alk is swinging because the y-axis goes from 8.3 to 8.8. If you adjust the scale to 7 - 11, what reefers usually target, the "swing" looks miniscule:

View attachment 2996555

Yeah I get that but the swing I'm seeing from ~8.4 to ~8.7 is repeating and seems real and although relatively small I'd still like to understand the science behind it. I understand that the kalk is raising alk so the 6am "spike" makes sense to me but I can't make sense of the 6pm "spike".

 

[90's reefer]

I think you are overthinking this one. Most people would love to have that swing. Its just usage vs adds that your graph shows.

No graph but I dose my 45 with 20ml of esv 1&2 2× a day by hand.
Morning alk is 7 add alk is 8.
12hrs later alk is 7 add and its back to 8.
So my system uses 2dkh a day. The graph would look crazy.

 

[chipmunkofdoom2]

I think you are overthinking this one. Most people would love to have that swing. Its just usage vs adds that your graph shows.

No graph but I dose my 45 with 20ml of esv 1&2 2× a day by hand.
Morning alk is 7 add alk is 8.
12hrs later alk is 7 add and its back to 8.
So my system uses 2dkh a day. The graph would look crazy.

I suspect the same is true in my tank. I dose limewater every 10 minutes on a dosing pump, all day, every day. I don't turn it off during the day or increase it at night. If I had a Trident, I bet the low would be about mid way through my photo period, the high would be just before the lights turn on in the morning, and the swing would probably be 0.5 dkh or more.

 

[90's reefer]

On my 80 I run a carx and I can easily hold a dkh of 7 +- .2dkh all day long.
I have never seen an issue with the by hand method. Your system will just get used to whatever method you use.
Dosing on a pump spread out through the day will offer a lower amount of flucuation.
I have had a 4 head dosing pump for a few years now and never set it up.
Same with apex as I ended up selling it because I never used it.

 

[Dennis Cartier]

Alk swings, and pH stability are some of my favourite things to manipulate, lol. A real parameter weenie's playground.

I previously used both a CaRx and kalk to constrain my tank pH between 8.3 and 8.4 24x7 and flatten the alk swing. I would stop the CaRx between midnight and 6 AM, and dose only kalk during that period, and then slow my kalk between 12 noon and midnight. It worked great, but I decided I wanted to see if I could remove the kalk to make the tank more sitter friendly.

Without the benefit of kalk, I just use the CaRx, but I modulate the flow based on the time of day to try to again minimize the alk swing and keep a small pH swing. Now I have my CaRx running at 30% of it's base flowrate between midnight and 6 AM, 65% between 6 AM and 3 PM, 75% between 3 PM and 9 PM, and finally 65% between 9 PM and midnight.

As you can see in my Alkatronic chart below, without the kalk, my pH swing now goes from 8.3 to 8.1, and my alk has about a .17 dKH swing (though I have had it down to a < 0.1 dKH swing often).

The alk swings in tanks are normally correlated with the light cycle. That is why I boost the flowrate of my CaRx, for the last 6 hours of my light cycle (3 PM - 9 PM). Otherwise I would get a dip, late in the day.

 

[JimWelsh]

I suspect the same is true in my tank. I dose limewater every 10 minutes on a dosing pump, all day, every day. I don't turn it off during the day or increase it at night. If I had a Trident, I bet the low would be about mid way through my photo period, the high would be just before the lights turn on in the morning, and the swing would probably be 0.5 dkh or more.

I'll just leave this here: https://www.reef2reef.com/threads/alk-swing-night.216823/page-2#post-3032727

 

[chipmunkofdoom2]

I'll just leave this here: https://www.reef2reef.com/threads/alk-swing-night.216823/page-2#post-3032727

That looks exactly like I thought it would!

 

[thatmanMIKEson]

Alk swings, and pH stability are some of my favourite things to manipulate, lol. A real parameter weenie's playground.

I previously used both a CaRx and kalk to constrain my tank pH between 8.3 and 8.4 24x7 and flatten the alk swing. I would stop the CaRx between midnight and 6 AM, and dose only kalk during that period, and then slow my kalk between 12 noon and midnight. It worked great, but I decided I wanted to see if I could remove the kalk to make the tank more sitter friendly.

Without the benefit of kalk, I just use the CaRx, but I modulate the flow based on the time of day to try to again minimize the alk swing and keep a small pH swing. Now I have my CaRx running at 30% of it's base flowrate between midnight and 6 AM, 65% between 6 AM and 3 PM, 75% between 3 PM and 9 PM, and finally 65% between 9 PM and midnight.

As you can see in my Alkatronic chart below, without the kalk, my pH swing now goes from 8.3 to 8.1, and my alk has about a .17 dKH swing (though I have had it down to a < 0.1 dKH swing often).

The alk swings in tanks are normally correlated with the light cycle. That is why I boost the flowrate of my CaRx, for the last 6 hours of my light cycle (3 PM - 9 PM). Otherwise I would get a dip, late in the day.

Well done! I want to get close to this

 

[Randy Holmes-Farley]

Main question: What is causing my alk to be higher at 6pm compared to 12am and 12pm?
Details: My Trident measures alk 4 times a day, 12am, 6am, 12pm, 6pm. At 6am and 6pm the alk is always higher than at 12am and 12pm. To maintain alk I'm dosing saturated kalk between 7pm and 7am so I understand why the 6am test measures high alk but why does the 6pm test also measure high alk when the kalk has been off for 11 hours before that? Similarly, why is alk lower at 12am than 6pm when kalk has been on for 5 hours prior to 12am?


All the peaks here are at 6am and 6pm, all the valleys are at 12am and 12pm.
View attachment 2996525

I'm not really seeing a perfect explanation for the alk changes you are seeing. I'd note the changes are pretty small and may be subject to complications that make the measured alk value imperfect. if you take more data points in a single day as an experiment, it might better help elucidate the issue, but IMO, is not necessary to do.