dendronephthya
New member
Some further information about my system discussed a few weeks earlier:
This is a 120 gallon tank with 10 inches of fine aragonite over a plenum.
Approximately 75 gallons/day is drained from the plenum and returned to the bulk water via TOM drip pump. The tank is illuminated 24 hours/day with 52 5 watt LEDs, and there is very little water flow. Topoff is with tap water and Kent's Iron and Manganese supplement, and fed 5-10 ml of a yeast based invertebrate food on occasion (q 3-7 days). Approx. 10 ml/week of silica "œwater glass" has been added. There is a heavy growth of microalgae and microalgae in the tank, being grazed down by Trochus snails. The purpose of this unusual setup is to attempt to generate a continuous plankton generation, as I have not been satisfied with the quantity of plankton generated by other refugium designs. There is excellent growth of plankton in this tank, and nitrates and phosphates are undetectable. The growth of plankton is especially heavy in floating mats present on the surface, and water drained from the surface (such as would occur in an overflow) is highly populated with plankton.
The problem I am having has to do with calcium and alkalinity. I would have thought that slow diffusion through a deep sand bed would DISSOLVE aragonite due to generation of carbon dioxide. At this time the exiting pH from the plenum (that is, the pore pH) is 8.4, and calcium is 300 and alkalinity is 5 kH even though I have been "œpouring in" the baking soda and some calcium chloride supplementation (and sometimes vinegar). In fact, these values seem to have been better since I stopped adding them, although not sure of this. Puzzling, yes?
This paper discusses pH of anoxic pore water in marine sediments http://www4.ee.bgu.ac.il/~pel/pdf-files/jour24.pdf The conclusion section states that pore pH in marine anoxic segments is controlled by 1) weak acids and bases which are the products of decomposition, 2) sulfate to sulfide reaction, 3) precipitation of metal sulfides, 4) precipitation of calcium carbonate. The first two drive the pH toward 7.0, the second two toward 8.4.
So, here's my question: will this system continue to precipitate calcium carbonate in the sand bed, or will it reach some equilibrium? (It hasn't after three months...). And- if no equilibrium will be reached, is there a way to fix this kind of system so it will perhaps liberate some ca/alk, such as switching to a quartz sand base, or adding elemental sulfur like a sulfur reactor and spare the sulfate utilization?
I appreciate any help here. I have great hopes for this type of simple natural system both for plankton generation and for filtration.
This is a 120 gallon tank with 10 inches of fine aragonite over a plenum.
Approximately 75 gallons/day is drained from the plenum and returned to the bulk water via TOM drip pump. The tank is illuminated 24 hours/day with 52 5 watt LEDs, and there is very little water flow. Topoff is with tap water and Kent's Iron and Manganese supplement, and fed 5-10 ml of a yeast based invertebrate food on occasion (q 3-7 days). Approx. 10 ml/week of silica "œwater glass" has been added. There is a heavy growth of microalgae and microalgae in the tank, being grazed down by Trochus snails. The purpose of this unusual setup is to attempt to generate a continuous plankton generation, as I have not been satisfied with the quantity of plankton generated by other refugium designs. There is excellent growth of plankton in this tank, and nitrates and phosphates are undetectable. The growth of plankton is especially heavy in floating mats present on the surface, and water drained from the surface (such as would occur in an overflow) is highly populated with plankton.
The problem I am having has to do with calcium and alkalinity. I would have thought that slow diffusion through a deep sand bed would DISSOLVE aragonite due to generation of carbon dioxide. At this time the exiting pH from the plenum (that is, the pore pH) is 8.4, and calcium is 300 and alkalinity is 5 kH even though I have been "œpouring in" the baking soda and some calcium chloride supplementation (and sometimes vinegar). In fact, these values seem to have been better since I stopped adding them, although not sure of this. Puzzling, yes?
This paper discusses pH of anoxic pore water in marine sediments http://www4.ee.bgu.ac.il/~pel/pdf-files/jour24.pdf The conclusion section states that pore pH in marine anoxic segments is controlled by 1) weak acids and bases which are the products of decomposition, 2) sulfate to sulfide reaction, 3) precipitation of metal sulfides, 4) precipitation of calcium carbonate. The first two drive the pH toward 7.0, the second two toward 8.4.
So, here's my question: will this system continue to precipitate calcium carbonate in the sand bed, or will it reach some equilibrium? (It hasn't after three months...). And- if no equilibrium will be reached, is there a way to fix this kind of system so it will perhaps liberate some ca/alk, such as switching to a quartz sand base, or adding elemental sulfur like a sulfur reactor and spare the sulfate utilization?
I appreciate any help here. I have great hopes for this type of simple natural system both for plankton generation and for filtration.
