Belgian Anthias
Valuable Member
I do understand the difference between CO2 consumption and carbonate consumption and the resulting effects on alkalinity and pH.
As Halimeda does not use system alkalinity ( carbonate) but CO2 for me it is logical one must take into account the CO2 consumption and its effect on pH. The production of bicarbonate, and precipitation into calcium carbonate within the private environment between cells, will only consume system calcium and CO2, supplied by the surrounding waters, this way removing calcium and no carbonate.
If we measure alkalinity we measure system water alkalinty which is an average of everything what has and is taking place.
The driving force for coral calcification is CO3, for Halimeda phothosynthetic driven calcification it is CO2.
It makes a big difference if the processes take place in a closed and private environment, without depleting system alkalinity, between the cells, as it happens in Halimeda. Of course, the chemistry is the same but it is limited to the provided space, Halimeda calcification uses carbonate first produced only in that little private space by CO2 exchange and consumption for photosynthesis, It is the intention harvesting the cultivated Halimeda removing everything from the system
As far as I know, already in the 60ties it was known Halimeda did it differently but it was not yet known how. Stark and Co conluded: Halimeda opuntia and Halimeda discoidea show a stimulation of incorporation by light as well as a diurnal rhythm under identical conditions of illumination. Both phenomena parallel the rhythm of chloroplast migration within the plant. Calcification is also stimulated by the addition of carbon dioxide. ( which is not the case in corals) Such evidence clearly indicated a light-linked mechanism that could involve photo-synthesis. However other metabolic processes, such as respiration, are also implicated. Aeration alone accelerates calcium incorporation. Nitrogen sources inhibit the incorporation of calcium during the day, indicating that cellular ammonia production is probably not responsible for precipitation. The differential wash-out rates of calcium absorbed during the day compared to those at night support the concept of a 2-step mechanism for calcification. (Stark LM, Almodovar L, Krauss RW. FACTORS AFFECTING THE RATE OF CALCIFICATION IN HALIMEDA OPUNTIA (L.) LAMOUROUX AND HALIMEDA DISCOIDEA DECAISNE(1). J Phycol. 1969;5(4):305-312. doi:10.1111/j.1529-8817.1969.tb02619.x)
Halimeda was commonly used in the seventies, after we changed the filter sandbed for oyster shell grit in our bio-filters , the difference between using Halimeda or Caulerpa was noticed. Also, buffering the water was suddenly not that difficult anymore, and we could not use anymore the decreasing period between the need for buffering the water to decide to do expensive water changes. So water changes became rare. Our guide till then was pH and hardness and the decreasing period it stayed buffered between corrections, till we had the means for measuring the nutrient content later in the seventies.
We then did not know why because we were not chemists. Our only guide was Frank de Graaf.
Frank De Graaf. Handboek voor het tropisch zeeaquarium. Tweede druk. A.J.G. Strengholt N.V. Amsterdam, 1969. And he did explain it correctly, taking into account what was known then. The book, still very useful for learning the basics to a nonchemist, was translated in English Graaf, Frank de. Marine Aquarium Guide. Harrison, N.J.: Pet Library, 1973.
Now we do know why because some people looked for answers and had the means.
Maby it is not correct to speak of system alkalinity consumption based on calcium carbonate consumption in an ongoing changing environment of a closed aquarium system?
Here it is only about managing calcium without effecting system alkalinity much, provide a stable environment without the use of chemicals.
And I am still convinced Halimeda removes calcium without consuming system alkalinity. Doubts? Try it out!
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