Rising alkalinity without dosing

[sculpin01]

Hi,

I have a relatively new system (420 gallons total) I set up recently with extremely low bioload currently. I have an Alkatronic/Dosetronic on it that initially was having to dose calcium/alkalinity (B-ionic) every 2-3 days to maintain a level of 7.8-8.0. This went on for more than a month until the last dose 8 days ago, following which the alkalinity increased to 8.15 and the Alkatronic has not dosed any of the alkalinity solution since then. However, my alkalinity has started to slowly climb on its own and is currently 8.6 (see below). I have double checked this with Hanna and it is accurate. I am using no other alkalinity supplements but am having to add Neophos and Neonitro to maintain appropriate nutrient levels.

Two questions,

1) Is the Neophos somehow displacing carbonate adherent to calcific rock leading to increased alkalinity?
2) I have a 1 M solution of HCL. How much would I need to add on a 420 gallon system to decrease the alkalinity back to 8.0?

Thanks!

Mike

 

[KStatefan]

Is your Nitrate going down? if so that will raise Alk.

Better way to word that is anything consuming nitrate will increase alk.

 

[sculpin01]

Nope. It is stable at 5 ppm with daily dosing of 20 cc of Neonitro.

 

[Randy Holmes-Farley]

Yes, but nitrate is being net consumed and that adds alkalinity.

 

[sculpin01]

Interesting. How do I lower my alkalinity?

 

[Randy Holmes-Farley]

Interesting. How do I lower my alkalinity?

You can add an acid along with the nitrate, use amino acids instead of nitrate, or do water changes with a lower alk mix.

It's a shame that Brightwell doesn't warn about this.

 

[sculpin01]

20 cc of 1 M HCl to start with maybe?

 

[Randy Holmes-Farley]

20 cc of 1 M HCl to start with maybe?

to what, the tank? I was think more along the lines of some acid in the nitrate dosing solution to continually offset the rise. Significant acid the the tank risks a big oH drop. There are a couple of threads detailing using acid in this forum.

 

[sculpin01]

As an update, 55 ml of 1 M HCl later (spaced out in four doses), alkalinity and pH are finally making a downturn from 8.65 dKH to 8.54 dKH.

I am considering switching to 1 M sulfuric acid from HCl to lessen impact to salinity.

 

[Randy Holmes-Farley]

As an update, 55 ml of 1 M HCl later (spaced out in four doses), alkalinity and pH are finally making a downturn from 8.65 dKH to 8.54 dKH.

I am considering switching to 1 M sulfuric acid from HCl to lessen impact to salinity.

The latter sentence is wrong. Neither will have an important effect on salinity, but sulfuric will have a larger effect per unit of alk depleted since sulfate weighs more than twice as much as chloride.

What size is this tank?

 

[sculpin01]

420 gallons. Could you clarify "larger effect per unit of alk depleted"? Are you referring to the pH?

 

[Randy Holmes-Farley]

420 gallons. Could you clarify "larger effect per unit of alk depleted"? Are you referring to the pH?

No. All acids that you might use have exactly the same pH drop per unit of alkalinity depleted.

I'm referring to the amount of salinity rise (which is very small and not a real consideration) per unit of alk depleted. Sulfuric acid gives a slightly higher salinity boost per unit of alk depleted because the residual counterion in sulfuric acid (sulfate; mw = 96 g/mole) is much heavier than in hydrochloric acid (chloride, mw = 35 g/mole).

 

[Randy Holmes-Farley]

1 M HCl effectively has a negative alkalinity of 1,000 meq/L, or negative 2,800 dKH.

If you add 55 mL of it to 400 gallons (1,510,000 mL) of water, it depletes alk by 2,800 x 55/1,510,000 = ~0.1 dKH, as you observed.

 

[sculpin01]

Thanks for the help!

BTW, is the alkalinity increase from Neonitro secondary to a biological process or is the solution alkaline? I’m impressed by how much of an effect relatively small volumes have on alkalinity.

 

[Randy Holmes-Farley]

Thanks for the help!

BTW, is the alkalinity increase from Neonitro secondary to a biological process or is the solution alkaline? I’m impressed by how much of an effect relatively small volumes have on alkalinity.

It's secondary to the biological process. The boost should be 2.3 dKH for each total of 50 ppm of nitrate added. Every nitrate ion added results in one bicarbonate ion.

I discuss the process here:


When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley - Reefkeeping.com

from it:


When this nitrate proceeds further along the nitrogen cycle, depleted alkalinity is returned in exactly the amount lost. For example, if the nitrate is allowed to be converted into N2 in a sand bed, one of the products is bicarbonate, as shown in equation 2 (below) for the breakdown of glucose and nitrate under typical anoxic conditions as might happen in a deep sand bed:

(2) 4NO3- + 5/6 C6H12O6 (glucose) + 4H2O --> 2 N2 + 7H2O + 4HCO3- + CO2
In equation 2 we see that exactly one bicarbonate ion is produced for each nitrate ion consumed. Consequently, the alkalinity gain is 0.8 meq/L (2.3 dKH) for every 50 ppm of nitrate consumed.

Likewise, equation 3 (below) shows the uptake of nitrate and CO2 into macroalgae to form typical organic molecules:

(3) 122 CO2 + 122 H2O + 16 NO3- --> C106H260O106N16 + 138 O2 + 16 HCO3-
Again, one bicarbonate ion is produced for each nitrate ion consumed.

 

[jbrady429]

I realize this thread is a couple of months old, but it is exactly what I needed right now. I have been lowering nitrates by dosing phosphate and carbon, and have experienced the same “mysterious” alkalinity rise. I had no idea that the nitrate reduction process was causing the alkalinity rise. Thank you everyone for educating me! This is awesome!

 

[sculpin01]

BTW, I continue to dose 1 M HCl to control this, without apparent adverse sequelae.

 

[Randy Holmes-Farley]

I realize this thread is a couple of months old, but it is exactly what I needed right now. I have been lowering nitrates by dosing phosphate and carbon, and have experienced the same “mysterious” alkalinity rise. I had no idea that the nitrate reduction process was causing the alkalinity rise. Thank you everyone for educating me! This is awesome!

You're welcome.

Happy Reefing!

 

[jbrady429]

BTW, I continue to dose 1 M HCl to control this, without apparent adverse sequelae.

How do you dose your HCl? Do you use a dosing pump, or do you mix it in with something else you’re dosing?

 

[sculpin01]

Dosing pump. At this point, it’s only when I have an unexpected pH spike. I just bought 1N HCl off of Amazon. Worked great.