Calcium and alkalinity balancing

Junkie · Jan 8, 2015

Randy, first and foremost I want to thank you for all the articles you have written and the wealth of information you freely share with this hobby. You are an invaluable resource to all of us that maintain reef tanks. I have been re-reading many of your writings, being that I'm paying more attention to my tank after some long term slacking. Although, I'm wondering about the balance of calcium and alkalinity. Is there direct numbers as to which calcium and alkalinity should balance at or can you force them to stabilize at any level. For instance, my calcium is at 450 ppm and my alkalinity is at 2.9 Meq/L. With that calcium level should my alkalinity be higher or is it fine as is? By adding esv two part won't my calcium raise as well? At 450ppm I don't really want it going much higher. Also, for reference I use oceanic salt and my mag is at 1420 and salinity is at 1.023. Again, thank you for for all you do and sorry if I missed the answer in something you have already written.

Randy Holmes-Farley · Jan 8, 2015

Thanks very much. I'm happy to try to help.

A two part should add about 18-20 ppm calcium for each 1 meq/L of alkalinity, which is also the ratio that corals use them.

So if you use B-ionic to boost the alk to 3.4 meq/L, calcium will only rise to about 460 ppm, which is fine.

Likewise, if you let the alk drop to 2.4 meq/L, calcium will only have dropped to about 440 ppm. At that point you can use the B-ionic two part to get back exactly where you are now, which is also fine.

If you want calcium lower than it is, just use only the alk part while letting calcium decline.

Make sense?

mike007 · Jan 8, 2015

Your alk. needs to be around 3.5 with ca. at 450. your salinity should be 1.026. you probably need to raise salinity slowly.

Junkie · Jan 9, 2015

Randy, yes makes sense. More what I was looking for was where mike007 got those numbers? Is there a chart or a formula that dictates where alkalinity level should be in reference to calcium? I was reading in one of your articles that by only adding the alkalinity of a two part to maintain alkalinity at a certain level is like "chasing a mirage" and therefore I'm interpreting I should be adding both parts of the two part. But should I bring my alkalinity up to a certain level and at that point I will have both calcium and alkalinity deplete at a 1:1 ratio resulting in less/equal daily fluctuation in alkalinity as well as calcium? At this point I have been adding 7.5ml of only alkalinity to counter the approximately 5ppm daily swing in alkalinity.

Randy Holmes-Farley · Jan 9, 2015

FWIW, the "balanced" values is not (or at least should not) be a goal. It is just NSW levels (2.5 meq/L, 420 ppm) +/- alkalinity and calcium in the same ratio that corals use it. So in that sense, if alk and calcium were high, you could let corals consume it until you got back to NSW levels.

But in terms of a goal, say calcium is 500 ppm. Does that mean it is "desirable" for alkalinity to be at the balanced level of 6.5 meq/L? No.

Balanced does not mean those values are easier to maintain. The lower both values are, the easier it is to maintain.

mike007 · Jan 9, 2015

370 ppm to 1.4 dKH
380 ppm to 2.8 dKH
390 ppm to 4.2 dKH
400 ppm to 5.6 dKH
410 ppm to 7 dKH (natural seawater)
420 ppm to 8.4 dKH
430 ppm to 9.8 dKH
440 ppm to 11.2 dKH
450 ppm to 12.6 dKH
460 ppm to 14 dKH.