How can DKh be imbalanced from Ca?

[Bulldog88]

I'm trying to figure out how my alkalinity if staying at 7!

Corals are happy, but my alkalinity was typically around 9.
Ca-450ppm
NO3- 4ppm
PO4- .02
Mg-1300
Salinity- 1.026
Ph- 8.2

I used the reef calculator last night and added some baking soda according to the tank volume to increase by 0.5 and recently tested and no change in Dkh. 15 gallon frag tank with a 10g sump. Several sps frags that are colorful and doing well. Seems like growth is going well as well.
Any ideas out there?

 

[LordDarth Bane]

Ca and CO3 (dKH) are not always comsumed in the 1:1 ratio. We used to assume that just because the coral skeleton, CaCO3 is 1:1.

For example, algae, both macro and micro need CO2. If there is not enough CO2 present in the water they would use CO3 to get the CO2 as well. In this case, dKH would drop faster than Ca.

Coralline algae use lots of Mg also.


btw, why you want to raise dKH from 7 to 9?

 

[Bulldog88]

Ca and CO3 (dKH) are not always comsumed in the 1:1 ratio. We used to assume that just because the coral skeleton, CaCO3 is 1:1.

For example, algae, both macro and micro need CO2. If there is not enough CO2 present in the water they would use CO3 to get the CO2 as well. In this case, dKH would drop faster than Ca.
Coralline algae use lots of Mg also.


btw, why you want to raise dKH from 7 to 9?

I assumed anything below 7 Dkh can lead to serious issues with SPS. I figured that it wouldn't be an equal 1:1 ratio, because hard corals need alk to utilize calicium correct? I was concerned why I'm seeing such a large decline in Dkh and Ca is staying stable.

 

[rovster]

My tank has done best both color and growth with dkh around 6-6.5. Been doing this a few years so have had time to observe. I believe every tank is different and its all about finding what works for yours. I used to keep it at 8 but had lots of issues then. Go figure. My tank is 90% acros most of which are at least minicolonies and lots that are 4-8" colonies.

 

[Cheapreef]

My tank has done best both color and growth with dkh around 6-6.5. Been doing this a few years so have had time to observe. I believe every tank is different and its all about finding what works for yours. I used to keep it at 8 but had lots of issues then. Go figure. My tank is 90% acros most of which are at least minicolonies and lots that are 4-8" colonies.

Just out of curiosity. Are you running a ULNS for that low of ALK? What issues were you seeing when keeping it in the 8ish range?