Question about calcium and other additives.

[pegasus]

I have, for the past 35 years, attempted to maintain a balance between Calcium and Alkalinity for reef tanks. Here are my thoughts:

Corals and other Calcium carbonate builders use Calcium and Carbonate in nearly the same proportion. So when 100ppm of Calcium is used, about 100ppm of Carbonate is used.

It just makes sense to me to keep them balanced or one could drop too low for the corals. As a starting point let's just say that 280ppm Calcium is where corals stop growing and start dissolving and 25ppm carbonate (Bicarb counts) is the level for Alkalinity.

I completely agree... Cal and Alk should be balanced. And you are correct when you say that corals use Calcium and Carbonate in nearly the same proportion. That very point is what I failed to express in my previous post. No two tanks are exactly the same, and the amount of Cal and Alk consumed by individual tanks will vary. The recommendations for using equal amounts of each (50/50) is simply a starting point, and each system will have to be adjusted to what it consumes. I find that I have to dose slightly more Alk than Cal to keep my levels consistent. That is why I can't rely on a chart that says if Cal is "X", Alk should be "Y". The only chart I can rely on is my log book that shows actual consumption. While it would be ideal to have both Cal and Alk in amounts that would allow both to run out at exactly the same time, I find it much easier to make sure both are within "usable" range. In other words... just don't let either fall below "usable" level(s). My view is that as long as there's enough of each (without over-saturation), everything will be fine... as long as levels are consistent. I think the majority of hobbyists will find this a much more achievable goal than to negotiate the formulas it would take to make sure both elements are added at the "perfect ratio". While test kits can put you "somewhere in the ballpark", none of them are going to be accurate enough to give a precise enough measurement to know exactly how much to dose. Kits get you close, and then it's trial-and-error as you adjust dosages. That alone is enough to drive most people mad, and to try to come up with matching numbers on top of that? Even if you do come up with the proper formula, the formula will have to be adjusted in a week or two to compensate for growth... or something as simple as adding another stony coral. While it may not be the most precise method, keeping Alk, Cal, and Mag within the proper range(s) is providing good growth and health for all my corals. I'll leave the number crunching for the rogue scholars to figure out... lol!