A question of "Balance"

[Hobster]

Randy,

I have been dosing 1/2 gal of Limewater for topoff daily. It appears to be maintaining by Ca at a level of 400. Total water volume is 50gal. The tank seems to be using 10 ppm per day. My question is: will the Alk naturally then want to seek a level of 2 meq/l as that is the balanced ratio? So no matter if I try to raise the Alk without increasing the Ca above 400, the Alk will drift back to 2 meq/l over say a week? (using the same limewater topoff) Don't know if that made sense:D
I have read and printed all your articles. still trying to get them absorbed.:)
Thanks

[Sloth]

Originally posted by Hobster
I have read and printed all your articles. still trying to get them absorbed.:)
Thanks Me too. I bet he's gonna ask you what your tank's pH is.:)

[Boomer]

My question is: will the Alk naturally then want to seek a level of 2 meq/l as that is the balanced ratio? So no matter if I try to raise the Alk without increasing the Ca above 400, the Alk will drift back to 2 meq/l over say a week?

That is more of on the lines what you see in an unbalanced system and is why we strive for a balanced system. In a balanced system it will remain more or less constant if the "components" are not being used. If you add some Ca or Alk they just go up and remain, if again they are not being used and if the addition or subtraction of the components is not to great and if the other ions are in balance. Balanced, by its true nature, in seawater is that all the ions are at or near their normal ratios. Off setting some of those ions, such as Mg, can have a negative affect on maintaining Ca and ALk. If one only added tap water for evaporation (no water changes), it wouldn't take to long ( 2-3 months) before the system becomes unbalanced.

[Hobster]

Boomer,

Mg is at 1350, Ca 400 and Alk 2.2ish (Salfert) My dosing of lime has kept the Ca at 400 and Alk at 2. ish, so based on the table that appears "balanced" If I up my ALk to say 4 meq/l and then just dose the same lime water should the Alk stay at 4? or will it eventually "balance" back to 2' ish??

[Boomer]

It should stay at that level of 4 but don't forget it will get consumed and go down. Alk will drop much more than Ca in a reef tank with calcifying organisms. Proportionally speaking, there is much, much more Ca that Alk. I forget the number but if you had say 400 mg / l Ca and attached all your Alk to Ca, there would be sill be like+ 300 mg / l Ca left in solution. It is quite common for many reefers to raise their Alk higher, say 3-4 meq / l and stay around 400 mg/ l Ca. Make sure your pH is within the target area of around 8.1 -8.3

[Randy Holmes-Farley]

There is nothing magic about the ratio between calcium and alkalinity.

IOW, the alkalinity will not "prefer" to be at any particular level as a function of the calcium level.

If you start with plenty of each (like NSW) and begin to calcify, then both will drop, and they will drop to the point where calcification (both by corals and abiotic precipitation become impossible. That might happen at about 380-400 ppm Calcum (down from 420 ppm) and 0.5-1.5 meq/l alkalinity (down from 2.5 meq/L).

At these levels, it is really the low alkalinity that is limiting calcification, and that's why folks never see it drop much below 1.5 meq/L, no matter where calcium is (unless it is very low and itself becomes limiting to calcification).

[Hobster]

OK, If I read this correctly, If I raise my alk to 4 and continue on my present dosing, then it should remain at 4. What seems to be happening is that my Ca remains stable at 400ppm but the Alk keeps going down. If corals use both at a ratio of 20:1 that what is out of balance? If lime is balanced then it seems it should maintain both the Ca and Alk. I guess where I am confused is that a ratio of 400 Ca to 4 Meq/l is not balanced (per the chart).
So will I need to raise Ca to say 425 in order to maintain Alk at 3-4???

Ps: Boomer, are you making your own Fireworks for the 4th?:D

[Randy Holmes-Farley]

Limewater will maintain calcium and alkalinity in roughly the right balance if you are adding enough. That's all I do. If you are not adding enough (or are adding too much so the pH gets too high, increasing abiotic precipitation) then you notice it first in alkalinity changes (drops).

So will I need to raise Ca to say 425 in order to maintain Alk at 3-4???


I think it would be good to have calcium at 390-450 ppm, but exactly where it is has no bearing on where alkalinity stabilizes.