Help with Alk/Ca balance?!?!

Andrew Schubert · Jan 19, 2019

So I've been dosing only bulk reef supply's kalkwasser to my tank for a number of reasons.

1) The tank is in the basement, and I wanted the increase of PH (before dosing Kalk my PH was around 7.8 to 8).Now it gets as high as 8.2.)
2) I wanted an easy for sure way to make sure to keep Alk/Ca in balance.

I've been dosing it through a kalk reactor via my ATO. I've been doing this for about a month now and my Alk seemed to stay pretty consistent right around 8.5. However over the last week my Alk has been decreasing into the mid 7s. HOWEVER, my calcium has remain completly constant through this decline at around 470.

From my studies and what I understand this makes no sense as one is dependent on the other. Over the passed 3 days I've just been dosing Alk part of bulk reef supplies 2part trying to get the Alk back in balance to where it was before this past week(my goal is 8.5).

Results... (Keep in mind the kalk reactor was still running during this time)

*For testing I used Hanna Checker for Alk, and Red Sea for Calcium*

On Jan. 16 my Alk was 7.9, so I dosed 35ml of Bulk Reef Supply soda ash, and on Jan. 17 now my Alk actually went down to 7.7.

On Jan. 17 I dosed 50ml more of Soda ash around 3 pm and check the results again at 10PM and it was at 8.5.

On Jan. 18 it was back down to 8, and then today it was down even lower once again to 7.7.

So as it stands today i'm at Alk 7.7 and Ca 470.

So my questions are....
1) Why would my Alk suddenly start dropping but my Ca stay in balance?
2) What should I do now? Just leave it until my Alk balances back out? continue dosing just Alk to get it back to where it was? Or should I does equal part Ca along with the Alk until my Alk gets back up into the 8s? So confused here!

rkpetersen · Jan 19, 2019

Hi. Nice looking tank. Using an ATO-based kalk reactor is very handy but it's limited to the amount of calcium and alk supplied in a day's evaporation water replacement, which can vary and at some times of the year might not be enough. Also you've got mostly small frags there now but as stony corals start to grow, you quickly reach the limit of what a kalk reactor can handle alone.

Regarding the association of calcium and alkalinity. It's not how most people think of it. Just because saltwater contains them at a ratio of around 450 ppm to 8 dKH, doesn't mean that they're consumed at the same proportion. Not at all. A whopping huge alkalinity change of 3 dKH only uses up 21 ppm of calcium! This is within the margin of error of most test kits, so it could look the same. And you could use up absolutely all the alk in the water and still have a calcium reading in the 300s.

Regarding dosing. I wouldn't try to make sense of the changing numbers you get when manual dosing, it will drive you nuts at it did me for awhile. Definitely try not to overreact to them. One factor that we all underestimate at first is abiotic precipitation, where calcium carbonate precipitates out on heaters, pumps, sump floor, sand in the DT, and elsewhere. This can be a huge consumer of alk. Doing manual dosing can actually make this worse, much worse, in addition to causing sizable acute pH swings which can damage your corals. As soon as you realize that you need 2-part (or just regular alk supplementing), imo it's time to get a dosing pump. Don't struggle with manual dosing for weeks or months as I once did. Everything smooths out with a doser, including much less abiotic precipitation.

Andrew Schubert · Jan 19, 2019

rkpetersen said:
Hi. Nice looking tank. Using an ATO-based kalk reactor is very handy but it's limited to the amount of calcium and alk supplied in a day's evaporation water replacement, which can vary and at some times of the year might not be enough. Also you've got mostly small frags there now but as stony corals start to grow, you quickly reach the limit of what a kalk reactor can handle alone.

Regarding the association of calcium and alkalinity. It's not how most people think of it. Just because saltwater contains them at a ratio of around 450 ppm to 8 dKH, doesn't mean that they're consumed at the same proportion. Not at all. A whopping huge alkalinity change of 3 dKH only uses up 21 ppm of calcium! This is within the margin of error of most test kits, so it could look the same. And you could use up absolutely all the alk in the water and still have a calcium reading in the 300s.

Regarding dosing. I wouldn't try to make sense of the changing numbers you get when manual dosing, it will drive you nuts at it did me for awhile. Definitely try not to overreact to them. One factor that we all underestimate at first is abiotic precipitation, where calcium carbonate precipitates out on heaters, pumps, sump floor, sand in the DT, and elsewhere. This can be a huge consumer of alk. Doing manual dosing can actually make this worse, much worse, in addition to causing sizable acute pH swings which can damage your corals. As soon as you realize that you need 2-part (or just regular alk supplementing), imo it's time to get a dosing pump. Don't struggle with manual dosing for weeks or months as I once did. Everything smooths out with a doser, including much less abiotic precipitation.

I have an Apex, so that was my plan to get the Apex doser once I needed it. Then I was planning on running both that way I could still keep the PH level up some as well. But I don't get the sense I need one yet as my Ca has remain stable at 470. I guess that's where its confusing. One the one hand you say 3dkh = 21ppm of calcium. However, you say we loose some dkh via other means. So if that is the case, then how can one know which is the case of why your Alk is decreasing? I've heard testing Alk daily is a more accurate assesment of your tank than Ca (as the reason you mentioned). However, it seems then that your change in Alk cannot be completely be a reliable test to the balance of Ca in your tank.

rkpetersen · Jan 20, 2019

Andrew Schubert said:
However, it seems then that your change in Alk cannot be completely be a reliable test to the balance of Ca in your tank.

This is correct for the reason I gave; changes in alk level will generally not give you any useful information about the corresponding calcium level. There really is no need to 'balance' the calcium level against the alk level in any case; just keep it in the proper range. Some people don't routinely test calcium at all, just alk.

Andrew Schubert · Jan 20, 2019

rkpetersen said:
This is correct for the reason I gave; changes in alk level will generally not give you any useful information about the corresponding calcium level. There really is no need to 'balance' the calcium level against the alk level in any case; just keep it in the proper range. Some people don't routinely test calcium at all, just alk.

So I guess that's where I dont get it. If Alk is not a direct correlation to Ca then how does testing Alk gives us any indication of the Ca in the tank? I've heard that too that testing Alk is so much more important than testing Ca but now I'm confused as to why.

rkpetersen · Jan 20, 2019

Any time alk and calcium are consumed together, whether from a coral growing or from precipitation on a heater, the resultant drop in alk is much much greater than the corresponding drop in calcium. No one can even accurately measure at home the expected change in calcium from a 1 dKH drop in alk. Since the alk is the much more sensitive indicator and therefore can fluctuate more, it's the one to keep an eye on. If you can keep your alk stable, you will generally have little to worry about as far as calcium level.

Andrew Schubert · Jan 20, 2019

rkpetersen said:
Any time alk and calcium are consumed together, whether from a coral growing or from precipitation on a heater, the resultant drop in alk is much much greater than the corresponding drop in calcium. No one can even accurately measure at home the expected change in calcium from a 1 dKH drop in alk. Since the alk is the much more sensitive indicator and therefore can fluctuate more, it's the one to keep an eye on. If you can keep your alk stable, you will generally have little to worry about as far as calcium level.

This article is pretty informative that I just found ...http://reefkeeping.com/issues/2004-05/rhf/

Andrew Schubert · Jan 20, 2019

Andrew Schubert said:
This article is pretty informative that I just found ...http://reefkeeping.com/issues/2004-05/rhf/

Makes me wonder if my recent change in Alk has to do with dosing red sea Trace colors. I know one of the elements is borate that is dosed, and that article mentions borate can mess with alk levels.