Alkalinity Dosing

[GargLabGT]

Hi all,
I was wondering what the best approach is to alkalinity dosing. Currently, I have the 2-part Calcium and alkalinity at my disposal (https://www.amazon.com/Red-Sea-Foun...rds=red+sea+alkalinity&qid=1617899862&sr=8-23). I also have an 11 gallon tank with about 9 gallons of water actually in it.
After dKH testing with Hanna Electronic alkalinity tester, I notice that quite a lot of alkalinity is consumed per day, around 1.5 to 2 and usually bottoms out at around 5 or 6. The tank has been cycling for a couple months with the nitrogen cycle completed a while ago. Added ammonium chloride has kept bacterial population stable. Other than this, there is 0 fish or coral or any non-microbial livestock in the tank. As an example of my situation, I performed a 90% water change because I over dosed ammonia, the dKH was 9. After a few days, the dKH was 6. In addition to dosing practices, what could be in the tank that consumes so much alkalinity?

 

[ichthyoid]

The oxidation of ammonium (NH3+) by nitrifying bacteria to nitrate (NO3-) releases 3 H+ ions (acid) in the process.

Alkalinity ions in the tank water (OH-) react with that released acid to form water, as in the following equation-

3 OH- + 3 H+ —> 3 H2O

That’s what is consuming the alkalinity

 

[jcook54]

The oxidation of ammonium (NH3+) by nitrifying bacteria to nitrate (NO3-) releases 3 H+ ions (acid) in the process.

Alkalinity ions in the tank water (OH-) react with that released acid to form water, as in the following equation-

3 OH- + 3 H+ —> 3 H2O

That’s what is consuming the alkalinity

Well this certainly is better than my standard "other stuff consumes alk" explanation. Thanks! I never really knew why or how but it certainly is true. Corals may consume calcium and alk is a specific ratio but I've always had to dose more alk than calcium. You've got a great feel for how much the tank is consuming and I would encourage you to dose daily in order to eliminate the swings that you're seeing. It can be a bit of a bugger on a smaller tank because an auto dosing setup can be nearly as big as the system your dosing.

 

[ichthyoid]

After checking, I got it wrong.

It’s actually 5 H+ ions released, during the 2 steps of bacterial nitrification ... Mea culpa

NH3+ + O2 —> NO2 + 3 H+

then

NO2 + H2O —> NO3 + 2 H+

So, for every molecule of ammonium oxidized, 5 H+ ions (acid) are released, which ultimately consume 5 OH- ions (alkalinity).

 

[Steve Burton]

I knew I wasn't crazy, common conception seemed to me that with no coral, alkalinity dosing would be unnecessary, but every tank I've cycled has required it to maintain stable alk. I'm glad my thought that it is due to nitrifying bacteria is substantiated.