Several years ago the original school of thought was the higher the alkalinity and calcium levels, the faster corals would grow? Scientifically this is seems to be true, it has even been tested on porties species corals and seems to work. It has been the standard advice given to many new reefers for years, alkalinity levels of 10-12 dKH.
Over the last few years many SPS reefers are finding that the high end of the dKH scale is not always better and that keeping alkalinity closer to NSW of 7-8 dKH has actually led to less issues of abiotic build up, excessive algae issues, RTN and even better growth results. From my personal experiences (7-8 dKH), I have found this also to be true. And during my research on this article I can now understand why my stability is better and why abiotic precipitation is much less.
Before we get into what is a good alkalinity level, let’s take natural seawater levels (NSW) for reference:
Alkalinity – 7 dKHPre 2006
Ca – 420 ppm
Salinity – 34-36ppt
pH – 8.0-8.3
Magnesium – 1280
Remember that the primarily idea pre 2006 was that raising alkalinity above NSW will increase calcification rates. Thus levels of a 10-12 dKH were recommended as a standard.
Typical Pre 2006 Reef System
Ca – 450-500 ppmSometime ago I did a study on the alkalinity changes amounts reef keepers over the past two years, although my data was very limited (using only Reef Central Tank of the Months) I still think the review was worth a look.
Alkalinity – 10-12 dKH
Salinity – 33 ppt
PH – 8.0 – 8.4
Magnesium – ????
While looking over several of the Reef Central Tank of the Months you notice a shift in thinking when it comes to alkalinity and calcium levels. Here are some of the results;
There seems to be a new trend of alkalinity levels getting closer to NSW. Over the first 15 months (2006-2007) alkalinity ranged from 8.7 - 9.8 dKH. During the last 6 months alkalinity dropped to ranges of 8.5-9.5. If I threw out the one guy running a 10 dKH the average would be a solid 8 dKH. Six months later I review this again with the new batch of TOTMS and again this trend continued with the last 7 tanks being, 8.5-9.5, 8-9, 9, 9, 9, 7, 8-9.
- 60% of the Reef Central Tank of the Months have an alkalinity level between 7-9 dKH.
- The most common level was between 8-9 dKH (25%)
- The average level of all the TOTMs was between 8.5 and 9.8 dKH (8.7 and 9.6 with a median score of 9.0)
In the last 6 months alkalinity is now at 8.4-8.8 with the median being 8.8-9.0. Almost 80% of the TOTM are NOT running a dKH higher than 9. In the last year only 1 person ran a dKH over 10.)
Variances – Stability is the Key
- 20 of the 25 tanks had a dkH lower than 10.
- Over 50% of the tanks have 9 dKH or lower. Again, looking over the last six month, now 16 out of 28 run lower than 10 dKH, 5 out of 28 run a dKH of 10 or over, and 7 run somewhere between 8-11 dKH. That is 57% run under a 9, 18% 10 or over and 25% run somewhere between 8-11 dkH.
Only 3 of the 25 tanks had a variance of more than 3 points - meaning the swing range is very low and alkalinity is very consistent and stable. Before reef keepers would say, “Somewhere between 8-11”. Now successful reefers know exactly where they are in terms of alkalinity, no more big swing listing of 7-11 they are exact numbers.
The largest swing listed was at 10 to 12 (3 points). In the last 2 years, no tank had an alkalinity variance greater than 3 dKH, again stable Alkalinity is key.
Todays Shift in Thinking Parameters
Calcium; 420 - 450 ppmConclusion
Alkalinity – 7-9 dKH
Salinity – 36 ppt
PH – 7.9 – 8.1
Magnesium – 1280-1300
We know the importance of what role alkalinity plays as a measurement of bicarbonate and how it does help stabilize pH. No more are general ranges of alkalinity, the more precise and stable the better the results.
There are many conclusion and ideas we can gain from the RC TOTM analysis alone. Closer to NSW alkalinity levels seems to be the trend, resulting is the appropriate calcium carbonate levels with less issues of algae, RTN, abiotic precipitations and with just as good or better looking corals and growth.
If you think about it, that should not surprise you. Natural seawater has an alkalinity of 7 dKH and corals grow very well. The increased alkalinity is only suggested as a way to make corals grow bigger, faster not the “gospel” measure that one can not go below. But this increased chance at increased growth comes at a price, more abiotic precipitation and less stable levels which leads to other issues.
I really believe that the closer to NSW levels of alkalinity is much easier to maintain, and thus resembles better success.
Reef Aquarium Water Parameters
Solving Calcium and Alkalinity Problems
Reef Chemical Calculator
Do-It-Yourself Magnesium Supplements
The Chemical and Biochemical Mechanisms of Calcification
Making Coral Skeletons
A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH
When Do Calcium and Alkalinity Demand Not Exactly Balance?
Chemistry and the Aquarium: What is Alkalinity?