I have run my reef (700liter with a SB over plenum in the sump (1-3mm grain, 40x50x10cm) and a fine 5cm SB in the main tank) for three years: During that time I have had constantly low calcium (300-350) and quite low KH as well (7-9). During the last year I have a Korallin reaktor that I have measured the output of calcium and carbonate to about 8 kg CaCO3/year. I have been quite puzzled why I can get the calcium up, but haven’t bothered much since my corals grew well.
When I started to get algae growing on the sandbed in the main tank, I decided to take out the sand, starting with the SB in the sump (plenum variant). Just a few days after the plenum SB was moved my KH had increased from 8 to 11. The sand in the main tank has been removed little by little (about 50% of it left). It has now been about a month from start of removal, and my values are KH=13, and Ca about 380.
I had read throughout hobby litterature that SB should be disolving CaCO3, but in this case it seems like it has been precipitated instead. I have never experienced any clumbing of the sandbed in this system. I have also read in marine chemistry textbooks, and tried to figure out was has happened, but I have not find any reason there either.
One reason can be that I noted that my salinity was quite low 1.021 and have raised it to 1.023 for now. Can this raise be the reason? Is the equilibrium of Ca and HCO3 in solution considerable lower in low salinity? Is higher salinity a block for CaCO3 to form, some type of crystal poison, making it easier to keep oversaturated levels of Ca and HCO3?
Anyone have any idea of why my sand seemed to eat CaCO3? Anyone had the same experience? Can anoxic areas result in elevated pH that in turn precipitates CaCO3?
/Klas
When I started to get algae growing on the sandbed in the main tank, I decided to take out the sand, starting with the SB in the sump (plenum variant). Just a few days after the plenum SB was moved my KH had increased from 8 to 11. The sand in the main tank has been removed little by little (about 50% of it left). It has now been about a month from start of removal, and my values are KH=13, and Ca about 380.
I had read throughout hobby litterature that SB should be disolving CaCO3, but in this case it seems like it has been precipitated instead. I have never experienced any clumbing of the sandbed in this system. I have also read in marine chemistry textbooks, and tried to figure out was has happened, but I have not find any reason there either.
One reason can be that I noted that my salinity was quite low 1.021 and have raised it to 1.023 for now. Can this raise be the reason? Is the equilibrium of Ca and HCO3 in solution considerable lower in low salinity? Is higher salinity a block for CaCO3 to form, some type of crystal poison, making it easier to keep oversaturated levels of Ca and HCO3?
Anyone have any idea of why my sand seemed to eat CaCO3? Anyone had the same experience? Can anoxic areas result in elevated pH that in turn precipitates CaCO3?
/Klas
