jeffbrig
Premium Member
(apologize for the long article)
I've been using a lazy man's 2-part additive system. Every week or so, I check the tank parameters, use jdieck's calculator to calculate amounts of CaCl and anhydrous sodium carbonate to correct any deficiencies, and I mix and dose solutions over a few of days.
With this last round of dosing, I noticed something strange. To begin with, the alk portion (baked baking soda) didn't cause the pH rise that I'm accustomed to seeing. I was trying to raise Alk from 6.7 to 10 dKH in a 250g tank, so we're talking a decent amount (60g, or 13tsp in ~1/2g RO/DI). Typically, when adding to the sump, my pH probe (also in the sump) will jump .3-.4 near instantly, then fade as the additive mixes away. This time I saw a rise of .02-.04 tops. I limited my addition rate based on past experience rather than follow the pH. I saw no localized precipitate cloud where the solution was added.
Dosing calcium was also interesting this time. The calcium part had visible precipitate this time, and I'm used to it being clear. I may have mixed the correction in a smaller volume of water than usual (150g / 30tsp in ~1/2 gal RO/DI), but I was still somewhat surprised. Ca came from the same bag of dowflake I've been using for 6 months or more, stored in an airtight salt bucket.
When I started dosing calcium, I noticed a faint milky precipitant blowing into the tank from the return outlets if I didn't add it in a slow trickle. Unusual for the Ca part, so I suspected low Mg. Yep, I was low, around 1050. So, I suspended Ca/Alk dosing and raised Mg to 1350 over the next few days. Went back to dosing Ca, noticed the same thing. My pH probe was reporting 8.15-8.25 over the weekend with the windows open to air out the house, so I recalibrated it yesterday and retested at 8.04.
After dosing all of the solutions, I retested all of the levels. My dosings were calculated to bring everything to 10 dKH, 425ppm Ca, and 1350ppm Mg. Ca measured 430 (close enough), Mag was right at 1350, but alkalinity fell way short at just 7.6 dKH.
So, what went on here? At first I suspected I may have switched the Alk and Ca containers by mistake, but the pH rise I observed when dosing from my Alk container seems to contradict that theory. My Ca was mixed in a container that has also mixed kalkwasser a few times, although I don't remember when the last time was, or if it was rinsed afterwards. I suppose kalk precipitant could explain the cloudiness I saw there.
So, how would I explain the smaller than normal pH rise of the alk, and why the levels didn't rise as much as expected? Could it be that my baked baking soda was not baked long enough to drive off all of the moisture? I know baking soda has more bulk, and requires about 50% more to effect the same change. Theoretically, if my alk was a mix of regular and anhydrous sodium carbonate, the pH change effects would cancel one another to some extent, right? But if I was 25% short of addtiive, that doesn't explain the alkalinity shortfall. Unless I also dosed more Calcium that needed, and both parts were consumed through precipitation and coral usage over the 2 days I was dosing.
What do you think?
I've been using a lazy man's 2-part additive system. Every week or so, I check the tank parameters, use jdieck's calculator to calculate amounts of CaCl and anhydrous sodium carbonate to correct any deficiencies, and I mix and dose solutions over a few of days.
With this last round of dosing, I noticed something strange. To begin with, the alk portion (baked baking soda) didn't cause the pH rise that I'm accustomed to seeing. I was trying to raise Alk from 6.7 to 10 dKH in a 250g tank, so we're talking a decent amount (60g, or 13tsp in ~1/2g RO/DI). Typically, when adding to the sump, my pH probe (also in the sump) will jump .3-.4 near instantly, then fade as the additive mixes away. This time I saw a rise of .02-.04 tops. I limited my addition rate based on past experience rather than follow the pH. I saw no localized precipitate cloud where the solution was added.
Dosing calcium was also interesting this time. The calcium part had visible precipitate this time, and I'm used to it being clear. I may have mixed the correction in a smaller volume of water than usual (150g / 30tsp in ~1/2 gal RO/DI), but I was still somewhat surprised. Ca came from the same bag of dowflake I've been using for 6 months or more, stored in an airtight salt bucket.
When I started dosing calcium, I noticed a faint milky precipitant blowing into the tank from the return outlets if I didn't add it in a slow trickle. Unusual for the Ca part, so I suspected low Mg. Yep, I was low, around 1050. So, I suspended Ca/Alk dosing and raised Mg to 1350 over the next few days. Went back to dosing Ca, noticed the same thing. My pH probe was reporting 8.15-8.25 over the weekend with the windows open to air out the house, so I recalibrated it yesterday and retested at 8.04.
After dosing all of the solutions, I retested all of the levels. My dosings were calculated to bring everything to 10 dKH, 425ppm Ca, and 1350ppm Mg. Ca measured 430 (close enough), Mag was right at 1350, but alkalinity fell way short at just 7.6 dKH.
So, what went on here? At first I suspected I may have switched the Alk and Ca containers by mistake, but the pH rise I observed when dosing from my Alk container seems to contradict that theory. My Ca was mixed in a container that has also mixed kalkwasser a few times, although I don't remember when the last time was, or if it was rinsed afterwards. I suppose kalk precipitant could explain the cloudiness I saw there.
So, how would I explain the smaller than normal pH rise of the alk, and why the levels didn't rise as much as expected? Could it be that my baked baking soda was not baked long enough to drive off all of the moisture? I know baking soda has more bulk, and requires about 50% more to effect the same change. Theoretically, if my alk was a mix of regular and anhydrous sodium carbonate, the pH change effects would cancel one another to some extent, right? But if I was 25% short of addtiive, that doesn't explain the alkalinity shortfall. Unless I also dosed more Calcium that needed, and both parts were consumed through precipitation and coral usage over the 2 days I was dosing.
What do you think?
