GaryP
Sat, 8th Nov 2003, 11:23 AM
I was in a LFS yesterday and got a couple of questions from one of the staff there. Admittedly this guy is a FW guy but I thought this was a bit odd and thought I'd pass these questions along for educational and discussion purposes. The staff member knows that I am chemist and that's why he approached me with these questions.
1. He said that he had a customer that wanted to know if putting limestone in his tank would cause his calcium to be to high. I told him that Calcium Carbonate, CaCO3, whether from limestone, LR, or LS is going to have minimal rates of dissolution due to the high pH that we operate SW aquariums. If it is dissolving, then the pH is probably way to low and he has bigger problems. Next I said that having calcium levels "too high" is rarely a problem, especially in a reef tank. I referred him to the chapters on water chemistry in Martin Moe's book, "Marine Aquarium Reference," which it turns out they didn't have in stock. I also said that I felt, but could not authoratatively verify, that there was some disolution of calcium in LR and LS from bacterial action. Bacteria may produce localized areas of low pH as a result of their metabolic by-products, such as organic acids like acetic acid. The general term for this is called micro environments. This is one of the reasons we have to add buffer to most tanks as it is used up in neutralizing these by-products as well as through depletion by corals as they use carbonate for skeleton building. I believe that some dissolution does occur in these localized areas, especially in the LS, particularly in the aerobic zone, even though the pH of the bulk water may be in typical pH ranges. My final point was to ask why his customer would want to use limestone in a SW aquarium. There is not sufficient porosity to produce good cultured LR. IMO Tufa is a much better way to go to produce cultured LR and I am actually helping a friend to do that now with a newly established tank.
2. OK this one was a little weirder. He said he had a customer that had heard that LR will absorb copper and later release it. I think the point is that there was a concern that copper may mysteriously peak after it has been removed. I told him that I wouldn't be suprised if that is true to some degree. The real point is to never allow copper into a reef tank in the first place. IMO the only time copper should be put in a tank is in a FO quarantine tank and then only in a very controlled manner. I also said that if copper was absorbed by LR then it would most likely slow leach back out at very low concentrations and could probably be removed by skimming or carbon filtration. The only way I could see a spike in copper concentration is if there was a huge dip in pH. Metals are usually made more soluble at lower pH's as I described in #1. I again emphasized that the emphasis sould be placed on not introducing copper to the tank in the first place by using proper acclimatization procedures.
OK, I just thought I would throw that out there. I hope I didn't lose some of you with all the chemistry. Sometimes I think someone needs to write a book on aquarium water chemistry for dummies. I realize that some of this gets a little to complicated for the majority of SW hobbyists.
Gary
1. He said that he had a customer that wanted to know if putting limestone in his tank would cause his calcium to be to high. I told him that Calcium Carbonate, CaCO3, whether from limestone, LR, or LS is going to have minimal rates of dissolution due to the high pH that we operate SW aquariums. If it is dissolving, then the pH is probably way to low and he has bigger problems. Next I said that having calcium levels "too high" is rarely a problem, especially in a reef tank. I referred him to the chapters on water chemistry in Martin Moe's book, "Marine Aquarium Reference," which it turns out they didn't have in stock. I also said that I felt, but could not authoratatively verify, that there was some disolution of calcium in LR and LS from bacterial action. Bacteria may produce localized areas of low pH as a result of their metabolic by-products, such as organic acids like acetic acid. The general term for this is called micro environments. This is one of the reasons we have to add buffer to most tanks as it is used up in neutralizing these by-products as well as through depletion by corals as they use carbonate for skeleton building. I believe that some dissolution does occur in these localized areas, especially in the LS, particularly in the aerobic zone, even though the pH of the bulk water may be in typical pH ranges. My final point was to ask why his customer would want to use limestone in a SW aquarium. There is not sufficient porosity to produce good cultured LR. IMO Tufa is a much better way to go to produce cultured LR and I am actually helping a friend to do that now with a newly established tank.
2. OK this one was a little weirder. He said he had a customer that had heard that LR will absorb copper and later release it. I think the point is that there was a concern that copper may mysteriously peak after it has been removed. I told him that I wouldn't be suprised if that is true to some degree. The real point is to never allow copper into a reef tank in the first place. IMO the only time copper should be put in a tank is in a FO quarantine tank and then only in a very controlled manner. I also said that if copper was absorbed by LR then it would most likely slow leach back out at very low concentrations and could probably be removed by skimming or carbon filtration. The only way I could see a spike in copper concentration is if there was a huge dip in pH. Metals are usually made more soluble at lower pH's as I described in #1. I again emphasized that the emphasis sould be placed on not introducing copper to the tank in the first place by using proper acclimatization procedures.
OK, I just thought I would throw that out there. I hope I didn't lose some of you with all the chemistry. Sometimes I think someone needs to write a book on aquarium water chemistry for dummies. I realize that some of this gets a little to complicated for the majority of SW hobbyists.
Gary