alkalinity swings

[fernalfer]

I have been dosing baking soda to bring my alk up a little. I have finally got it up to 9 dKh. I test before dosing and test the next day. Why is it my Alk always goes down 1 dKh every morning when i test but Calcium and Magnesium never change?

I have just 1 hammer, 3 zoas, and 1 green star polyp. What is consuming the Alk like that? and why can't i keep it stable.

 

[reefwiser]

To properly test alk it needs to be done before the lights come on and then right before the lights go off at night. This will give you the alk swing across the day. Corals calcify during the time the lights are on. Your hammer would be using the alk.

 

[dgrigor02]

Ca/MgIt levels are dropping its just the test kits are not sensative enough to pick up the change. 1 dkh the CA will drop 7ppm, magnesium is usually 1-3% of the calcium rate so approx .07ppm. Your test kits are not sensative enough to detect that small of a change so gives the illusion that it is not changing.

If you test over a large sample of time you will see it dropping. Most kits at best are 20ppm resolution then you account for human eye determining when the color change can easily turn that into a 20-40ppm variation.

It is very normal for a tank to use 1-2dkh of alkalinity per day. If you want to keep it more consistant thats when people stop dosing manually and automate it with a perstalic pump to add slowly throughout the day. Baking soda has a tendancy to lower pH temporarily so best to dose that during the day cycle. Soda Ash hs a tendancy to raise pH so best to dose that during the night cycle with pH naturally lowers.

 

[Randy Holmes-Farley Verified Community Expert]

I have been dosing baking soda to bring my alk up a little. I have finally got it up to 9 dKh. I test before dosing and test the next day. Why is it my Alk always goes down 1 dKh every morning when i test but Calcium and Magnesium never change?

I have just 1 hammer, 3 zoas, and 1 green star polyp. What is consuming the Alk like that? and why can't i keep it stable.

With a 1 dKH change in alk, you'd expect about a 6 ppm change in calcium and below 1 ppm magnesium. I expect you just cannot detect such a calcium change with a kit, and definitely cannot detect a magnesium change.

1 dKH per day is not that high, and is normal. Coralline algae, snails, clams, tube worms, corals, etc. all use calcium and alkalinity. If nitrate is rising, that too depletes alkalinity.