Question regarding changing Alk dosing times

Laith · Dec 3, 2018

I'm currently dosing Balling Light for Alk and Calcium and up to now have been using a doser that automatically spreads the dosing over a 24 hour period.

After measuring KH twice a day for several weeks I notice a build up overnight (when the Alk isn't being consumed) so I decided to reduce the dosing period of the Alk to starting two hours after lights come on through to two hours after lights out.

I think I know the answers to the questions I have but would like it confirmed:

1. Do I dose the same amount of Alk over the shorter period as I was over a 24 hour period?
2. Do I also change the dosing period of Calcium to match that of the new Alk dosing period?

All input appreciated!

DLHDesign · Dec 4, 2018

1) Your Alk consumption should remain constant with what it's been, so yes - I would keep the total volume dosed in a 24hr period the same.
2) You can, but I don't think you would have to specifically. Any calcium not consumed overnight should still be available for use once the lights are on again. At the same time; there's not really any reason I can think of to not shift the schedule to match.

As might be obvious, I would also suggest continuing the measurements of both Alk and Ca for a while after the change (and Mg as well if that runs close to the minimum levels in your tank). It may be that the higher concentrations that will result during the day could have an increase in uptake (e.g.; growth); something that may then require fine-tuning.

Laith · Dec 5, 2018

Thanks Dave... your answers confirm what I was thinking.

I've gone ahead and changed the Calcium dosing period to match the Alk dosing period and will keep an eye on the levels.

What I have already noticed since changing the Alk dosing period is that my Alk measurements are the same when I measure before lights on and at the end of the light period. Previously I was always seeing a 0.3-0.4 difference between the two measurements.

I like the more stable Alk levels. Let's wait and see if the corals feel the same!

Randy Holmes-Farley · Dec 8, 2018

I would not assume the alk demand will remain the same after the dosing time switch, but it is a good starting point.

Laith · Dec 8, 2018

Do you mean that changing the dosing period will change the demand for alk? Not sure how that would happen...

I know the demand for alk changes all the time depending on a variety of parameters and that is one reason the GHL KH Director is on my shopping list

. I will let it manage the alk dosing depending on the demand.

Randy Holmes-Farley · Dec 8, 2018

Laith said:
Do you mean that changing the dosing period will change the demand for alk? Not sure how that would happen...

I know the demand for alk changes all the time depending on a variety of parameters and that is one reason the GHL KH Director is on my shopping list . I will let it manage the alk dosing depending on the demand.

Several ways.

The actual alk level impacts the demand. It takes more each day to maintain 9 dKH compared to 8 dKH. Changing the dosing schedule may well change the alk (if it doesn’t, then why do it?) and that may change the demand. For example, 12 h at 6 dKH and 12 at 8 dKH may not have the same total daily demand for alk as steady 7 d KH.

Also, higher alk at the same time as corals want to take it up and/or at the same time pH is highest and so precipitation will be highest may give a different demand than the opposite of each of those things.

Laith · Dec 9, 2018

Good point regarding the 12h at 6 KH vs 12h at 8 KH.

However, why would it take more each day to maintain 9 than it would 8? The alk we are adding is to compensate for the reduction of KH during a certain period. If the uptake is 1 KH per day, then enough alk needs to be added to raise the KH by 1 per day. Whether your starting point is 7, 8 or 9 shouldn't have an impact on the amount of alk needed to raise the KH by 1?

Or are you saying that the uptake may be different if the KH is at 7 than it would be if the KH is at 9?

Laith

Randy Holmes-Farley · Dec 9, 2018

Laith said:
Good point regarding the 12h at 6 KH vs 12h at 8 KH.

However, why would it take more each day to maintain 9 than it would 8? The alk we are adding is to compensate for the reduction of KH during a certain period. If the uptake is 1 KH per day, then enough alk needs to be added to raise the KH by 1 per day. Whether your starting point is 7, 8 or 9 shouldn't have an impact on the amount of alk needed to raise the KH by 1?

Or are you saying that the uptake may be different if the KH is at 7 than it would be if the KH is at 9?

Laith

The uptake is not a fixed number. Both coral calcification and abiotic precipitation generally increase as the absolute alk value increases. They also increase as pH increases.