What salt are you using btw? Do you have pvc tubing incorporated into your setup?
Also strontium has been suspected to be purposely incorporated from what's been seen in research so far in the aragonite formation process, even to the point where a coral manipulates skeletal growth to incorporate or not. Might look into an additive if your salt doesn't provide enough. I think it makes a fair amount of sense that corals utilize it, it's easier to "manipulate".
In ground-breaking research, a team of scientists from Australia's ARC Center of Excellence for Coral Reef Studies, at the University of Western Australia and France's Laboratoire des Sciences du Climat et de l'Environnement, has shown that some marine organisms that form calcium carbonate skeletons have an in-built mechanism to cope with ocean acidification - which others appear to lack. Marine organisms that form calcium carbonate skeletons generally produce it in one of two forms, known as aragonite and calcite. The team found that those with skeletons made of aragonite have the coping mechanism - while those that follow the calcite pathway generally do less well under more acidic conditions. "The good news is that most corals appear to have this internal ability to buffer rising acidity of seawater and still form good, solid skeletons," said Professor Malcolm McCulloch of CoECRS and UWA. The aragonite calcifiers - such as the well-known corals Porites and Acropora - have molecular ‘pumps' that enable them to regulate their internal acid balance, which buffers them from the external changes in seawater pH. Read more from Asian Scientist Magazine at:
http://www.asianscientist.com/2012/...t-to-ocean-acidification-global-warming-2012/
Another couple points of interest that suggests incorporation or avoidance of strontium is not "chance":
Many marine organisms, including corals, build skeletons from calcium carbonate – in the form of calcite or aragonite. The current composition of seawater favors the formation of aragonite – but soft corals have a specific protein that allows them to form calcite skeletons instead.
https://www.sciencedaily.com/releases/2011/08/110816120828.htm
Effect of light and temperature on calcification and strontium uptake in the scleractinian coral Acropora verweyi
https://www.researchgate.net/public...e_in_the_scleractinian_coral_Acropora_verweyi
Using scanning electron microscopy, we observed different crystal morphologies of aragonite and calcite in a single juvenile skeleton. Quantitative analysis using X-ray diffraction showed that the majority of the skeleton was composed of aragonite even though we had exposed the juveniles to manipulated seawater before their initial crystal nucleation and growth processes. Our results indicate that the modern scleractinian coral
Acropora mainly produces aragonite skeletons in both aragonite and calcite seas, but also has the ability to use calcite for part of its skeletal growth when incubated in calcite seas.
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0091021
However, the change in atomic arrangements does change the list of impurities that can be easily included in aragonite. While calcite is commonly riddled with magnesium atoms, aragonite is typically found to be riddled with strontium atoms instead. Elements like barium and lead and a few others are also mixed in at times, but strontium is the most common of the bunch.
http://www.advancedaquarist.com/2011/10/chemistry
Thanks for any help or suggestions.
