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DT's_Reef
10/07/2009, 10:51 AM
I use a Profilux doser to dose BRS alkalinity and calcium solution. For some time, I've been dosing a 1:1 ratio.

Does it matter what the dosage ratio is? I say this because my alkalinity will slowly creep down to the 6 range when I really would like it in the 7 range, but my calcium level is perfect around 420-440.

Any harm in dosing 2 parts CA to 3 parts Alk? I just don't want parameters "fighting" with each other.

Thanks.

skimmerman100
10/07/2009, 11:23 AM
do you have a phosban reactor? if you do that can be the cause of the lower alk. just dose alk to raise it and check it every other day

DT's_Reef
10/07/2009, 11:29 AM
No, I do not have a reactor, but I do keep a bag of phosphate remover (Warner Marine High Capacity) in the sump. It's probably a few months old.

Randy Holmes-Farley
10/07/2009, 01:00 PM
I'd dose both equally unless calcium actually gets too high. Driving alkalinity up from 6 to 7 dKH will only boost calcium by 7 ppm. :)

flamron
10/07/2009, 01:00 PM
So, you try to keep your params at 7dkh and 440? But your Alk is dropping to 6. I'm betting your calcium is around 420 when you measure this, correct?

According to the reef calculator, an Alkalinity of 7dkh is in ionic balance when calcium is at 410ppm.

Calcium will fall ~7ppm for every 1dkh. I would say once you get everything balanced, boost your dosage amount by 10ml (for both parts) every 7-10 days and check your Alk frequently.

Hope this makes sense! (I'm not really sure if it does, LOL)

Fixed!

Randy Holmes-Farley
10/07/2009, 01:01 PM
20 ppm for each 1 meq/L. That's 7 ppm per dKH. :)

flamron
10/07/2009, 01:02 PM
do you have a phosban reactor? if you do that can be the cause of the lower alk. just dose alk to raise it and check it every other day

Randy,

Is this accurate? I have read a lot of conflicting posts about this.

DT's_Reef
10/07/2009, 01:16 PM
As long as the calcium is above 400, I'm not terribly concerned about this parameter. I'm mostly concerned about the alkalinity around 7. My pH meter basically lets me know when my alk is starting to dip.

So perhaps I should keep the 1:1 ratio, but increase the rate. My tank is 85g and I dose 48ml of each solution. Perhaps I'll increase it to 3ml per dose, but cut the # of dosings per day from 24 to 18 or 19....for a total of around 54ml per day each. Hmmm, I'll have to tinker a bit more and go from there.

Randy Holmes-Farley
10/07/2009, 02:13 PM
Is this accurate? I have read a lot of conflicting posts about this.

GFO can help induce precipitation of calcium carbonate, which can bring down both calcium and alkalinity a bit, but you notice it firs tin alkalinity. :)

I discuss it here:


Iron Oxide Hydroxide (GFO) Phosphate Binders
http://reefkeeping.com/issues/2004-11/rhf/index.htm

from it:


What else might iron oxide hydroxide do? Precipitation of CaCO3

Many aquarists using GFO have reported unusually extensive precipitation of carbonates on the solid GFO, and elsewhere in the system. Such precipitation can, for example, be a contributing factor in the caking of such materials, and can coat other surfaces in the aquarium. This precipitation can also contribute to a drop in alkalinity and possibly pH as it removes carbonate from the water column. The effect of calcium will be similar, but smaller on a percentage basis, with a drop of only 20 ppm calcium for every 1 meq/L (2.8 dkH) drop in alkalinity. Increased calcification by corals and coralline algae (possibly spurred by reduced phosphate) can also cause similar drops in calcium, alkalinity, and pH.

Dissolution of these precipitates with acid, accompanied by bubbling, indicates that these deposits are carbonates, and are most likely calcium carbonate since it is supersaturated in most reef aquaria (and in the ocean). Several factors may contribute to this precipitation. Many of these are rather straightforward. It is known, for example, that phosphate inhibits the precipitation of calcium carbonate. Much like the role that magnesium plays in seawater, phosphate binds to the growing calcium carbonate crystals, poisoning their surface against further precipitation of calcium carbonate. Many organic materials are also known to inhibit this precipitation. Near the surface of the GFO, and downstream from it, the organics and phosphate are expected to be lower in concentration than upstream from it. The reduction in concentration of these inhibitors may well permit increased abiotic precipitation of calcium carbonate on such surfaces.

Two more esoteric events may, however, be equally important. The first is that the local pH near the GFO surfaces may be higher than in the bulk solution. This effect arises as phosphate and other inorganic and organic ions displace hydroxide from the surface. Figure 2, for example, shows phosphate displacing two hydroxide ions. The net swap of HPO4-- for 2 OH- will raise the local pH. The supersaturation of calcium carbonate increases as the pH rises, driving the precipitation of calcium carbonate.

Another possible role may be played by the iron itself. GFO is not completely insoluble. The solubility of iron hydroxide in natural seawater is small, but still significant (0.02 - 2 ppb), although it is largely controlled by the availability of organic ligands.11-13 One interesting possibility lies in the way that soluble iron actually impacts the precipitation of calcium carbonate.

At high concentrations, iron inhibits the precipitation of calcium carbonate. While different researchers find different threshold concentrations for this inhibition (>25 ppm in one case,14>7ppm in another case15), it is a well established and studied phenomenon. The mechanism is believed to be the same as for magnesium, phosphate, and organics, which all poison the growing calcium carbonate surface.

At much lower concentrations, however, iron actually increases the precipitation of calcium carbonate by acting as a site for nucleation of new crystals. In one case this happened at 100 ppb dissolved iron, increasing the rate of scaling (the precipitation of calcium carbonate on surfaces) by about 60%.14 In another case, the induction time for precipitation (that is, the time it takes for precipitation to begin once the water becomes supersaturated) was reduced by 40% at 1.4 ppm iron and the overall precipitation rate was increased by 32% at 560 ppb (lower iron levels were not tested).15 These studies were carried out in freshwater, and I have not seen similar studies in seawater.

Is the natural dissolution of GFO important in the nucleation of calcium carbonate precipitation? I am not sure. But it is clearly one possible explanation that fits the observations of aquarists as well as known phenomena involving iron.