What's the ratio of calcium to alkalinity consumption?

[Cory]

My tank is starting to use a lot of bicarbonate. my montipora and frogspawn are pigs. I haven't bothered to check the calcium, but in a weeks time I've lost 2dkh of alk to these two corals. The monti frag is encrusting nicely on the rock. I'm surprised how quick it's growing, looks like it used 100ppm of calcium to build the new stone. But since I haven't checked calcium, what can I expect when corals grow? 1dkh to 20ppm calcium?

 

[UK_Pete]

From wiki:

One degree KH (dkh) is equal to 17.9 mg/l (ppm) CaCO3

CaCO3 mol weight is 100, calcium mol weight is 40, carbonate mol weight is 60. That means calcium carbonate is 40% calcium, 60% carbonate by weight.

So one dkh is 17.9 * 0.4 = 7.2 ppm calcium, and 17.9 * 0.6 = 10.7 ppm carbonate.

 

[Randy Holmes-Farley]

Hi Pete, I edited the quote in your post to put the 3 on the line with the CaCO so it showed CaCO3 correctly.

Calcium consumption is about 18-20 ppm for each 1 meq/L or 2.8 dKH of alkalinity (6.4-7.1 ppm calcium per dKH, as Pete indicated). The reason there is some variability is due to the variable incorporation of magnesium in place of calcium in the calcium carbonate structure. Different corals use slightly different amounts.

 

[UK_Pete]

Doh - forgot about the magnesium part! Thanks Randy

 

[Cory]

Ah that makes sense. Thanks guys! Of course other processes can also drop bicarbonate too right. Now that I recall it must hav been more like 8dkh in a weeks time. So 8x18-20 = 144 to 160ppm calcium! I'll test it tonight. Last I measured calcium it was at 420ppm, so there may be a big drop. I better test magnesium too.

 

[Randy Holmes-Farley]

There are a few other processes that might be happening that reduce alkalintiy, such as rising nitrate (not steady nitrate). But in a steady state reef, these may be minor.

I discuss them here:

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

 

[Joey Vagneur]

Randy this is an older post, but I have just re-read your above artical and feel like I may be dosing wrong. I currently dose your recipe #1, and seem to does 400ml of Alk solution per day and 280ml of calcium to my 110 total volume tank. Heavy sps. My Alk is always between 7-8 dKh and calcium is 400-410. Mag is 1350ish. I am increasing Alk so to get numbers up, but seem to not be able to. I have lots of pump precipitate and so feel I am dosing too much Alk and calcium. I know I am dosing out of balance.

How would you suggest correcting this? Get levels to target stop dosing and take daily tests to determine drop and then calculate daily alk consumption. Add that amount of 2 part daily?

 

[Randy Holmes-Farley]

One cause of the need for imbalanced dosing is water changes with a salt mix that doesn't match the tank.

What salt mix are you using?

What happens if you dose much less of the alk?

Sometimes people get into a cycle where precipitation starts and can be hard to stop.

 

[Joey Vagneur]

Randy thanks you for your response. I use IO reef crystals. Although I have not been as good with water changes. Maybe once every two months. I have not had need to. Parameters are stable and animals are all healthy.

I do dose via a doing pump that spreads this out through the day. 4 100ml doses. Calcium is in 3 doses. Alk and Cal are both over an hour apart. I dose into my sump. Flow could go up. I just recently tried to increase this.

When I stop the will both go down but it is gradual and not a drop off.

Any ideas or recommendations are appreciated I am going to be moving into a bigger tank and would want to start off with a correct dosing regime

 

[Randy Holmes-Farley]

How much alk per day is that in dKH?

 

[Joey Vagneur]

Good question, are you asking how much DKh is represented by my 400 ml dose or how much the tank drops per day? If I stop providing Alk it will drop by 1-1.5 per day until it reaches about 6 then it slows.

 

[Joey Vagneur]

Although it still drops or seems to by "happy" with my dose at 7-7.5

 

[Randy Holmes-Farley]

Good question, are you asking how much DKh is represented by my 400 ml dose or how much the tank drops per day? If I stop providing Alk it will drop by 1-1.5 per day until it reaches about 6 then it slows.

The dose is what I was asking. To guess how much you are really adding over the "likely" real demand by corals and such.

 

[Joey Vagneur]

Gotcha, so if I understand your recipe correctly a mixed solution of Baked baking soda of 2 1/4 Cups to 1 gallon of RO/DI should have a total value of 5300 dKH or 1900 meq/L. If my math is on there is about 3785.41 mL / gallon of water. So that would mean I would yield 1.4 dkh/ml of mixed solution??

If I am adding 400 ml/day I am adding 560 dKH to my system? I have to be incorrect here.

 

[Joey Vagneur]

So in looking at the reef calculator.. 400 ml should equate to about 5.6 dKh so my above math seems to have missed a division of the dkH somewhere.. but looks like if I set my 110 gallons of total water and set Randy's recipe 1 in order to get the calculator to require 400 ml I would need a change in dkh of about 5.18ish

 

[Joey Vagneur]

I cannot imagine my tank is using this much, and so accounts for the pump cleaning monthly...

As I said I am moving into a larger tank, with new equipment, so want to make sure I start off right, but would love to know how to balance my system and put it into a proper dosing amount. I could do a large water change, stop dosing and make daily corrections manually to see what I should be adding, then add that and see if the tank stabilizes..

Any other idea would be appreciated. Thanks randy, I love reading your articles... brings me back to Organic Chem..

 

[Joey Vagneur]

Last night when I measure Alk I was at 7.5 dKh and 425 calcium. I decided to raise my Alk from 400ml daily dose spread out over 4 doses of 100ml each to 115 ml per dose so about 460 ml total. I also. Increased calcium from 260 to an even 300.

Tonight I tested and I am at 7 dKh and 420Cal. I went down!?! Even after an increased dose. This leads me to conclude that indeed I have precipitation taking place that is mostly absorbing my 2 part. Tonight I balanced my calcium to Alk supplement so both are at about 460 each..

I feel something is off. Tank and sps are all happy but concerned with amount of 2 part being used as well as precipitation to pumps etc.

May try my stop dosing experiment. I am at a loss

 

[Aaron Atkinson]

I have a similar scenario which is proving very difficult for me: dosing more but watching alkalinity drop. How does one break the precipitation cycle?

 

[Joey Vagneur]

I hope Randy has a suggestion my thought process is to do 2-3 30% water changes over the course of a week. This ensures that my salt mix if mixed to proper salinity has helped add balanced levels of calcium back to the tank. During this time I am going to soak all pumps and my skimmer in acid to remove the calcium carbonate. Once I have accomplished this step I plan to stop all dosing and test daily for 2-3 days.This will allow my to hopefully get an idea of my true tanks consumption. Make 1-2 safe correction dose to achieve my target parameters then start with equal amount of 2 part based on the Alk demand as it is used faster. The make tweaks. Hopefully this balances the system.

I should note I read about calibrating my dosing pump to make sure the correct amount of solution is dispensed. I plan to also do this during the water change/deep clean stage..

 

[Aaron Atkinson]

Hello Joey, thanks for the reply. What I did was similar to you. Stopped all dosing for a week, conducted 20% water changes daily for 4 days. Checked the alkalinity drop for a few days without dosing. And upped the magnesium to about 1350 as well. When I restarted hand dosing to check stability, I was right back to seeing an alkalinity drop, roughly 0.3 or more the next day. I am loosing my mind at this point.

Further more, I have documented increased alkalinity "usage" at higher initial alkalinity. I read this is normal, but I feel trapped in a cycle which doesn't allow me to raise alkalinity. Put more in to raise, loose more, staring point becomes lower the next day. This is frustrating.

I did not clean off the heater or skimmer pump. The return pump I did earlier because it seized....I should clean the other stuff this weekend. Help would be appreciated.