Quote:
Originally Posted by crvz
Dripping kalk will not raise the alkalinity level directly, but it does have an affect. If you want to increase pH without adding chemicals, one option is to run some sort of refugium with macro algae, preferably on a reverse photoperiod (lights come on at night). This should help bolster the pH, as the macro algae will consume CO2 from the water column.
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Well,
actually... The extremely high pH of the kalkwasser solution as it drips into your seawater almost immediately creates a microenvironment that converts CO2 in the water column directly into bicarbonate at a 1:1 ratio to the amount of molar calcium that is introduced with the kalkwasser:
Ca(OH)2(solid) <-dissolved in water-> Ca++ + 2(OH)- + COOH <---> Ca++ + HCO3- + HOH
This solution can actually increase the pH of the solution because it removes the
real driver of pH in seawater, the concentration of carbon dioxide = the partial presure of dissolved CO2 = pCO2 in seawater. This is the same effect we expect from using photoautotrophs during perioids of light in the refugium, as they consume CO2 to make carbohydrates and decrease the pCO2 in seawater in the process as crvz already mentioned.
Ideally, the best way to prevent issues with chronically low pH is to prevent the accumulation of
CO2 (
typo edit-tdwyatt) in the water column. This is acheived by making sure there is good air/water exchange of gasses (open tanks without lids), surface agitation, good flow throughtout the tank, and low atmospheric CO2 above the tank water. As the reduction of high atmospheric CO2 above the tank water may not be possible in cold or hot climes during the summer and winter, running a pipe from the air intake for the skimmer to an outdoor source is a good alternative. Make sure to include an in-line filter of active carbon to prevent the unintentional introduction of aerosolized toxins and misc other airborne contaminants through the skimmer. This will reduce the effect of indoor high levels of CO2 that accumulate in most environmentally "tight" homes.
An interesting little test you can run to check for the significance of CO2 in your particular system is to take a quart mason jar, pour in a cup of your tank water, then go outside and fan some outdoor air into the jar. Seal the lid on the jar and agitate it vigorouly for 5 minutes. Open the lid, fan the air outside into the jar and repeat this procedure 4 times. After completion of the last cycle of agitation, place your pH probe into the seawater you've just processed and measure the pH value...
Basically what you've done is gas off the excess CO2 by using the outdoor air to drop your pCO2 saturation of the sample. Normally air outdoors is around
383 PPM for CO2, indoor home atmosphere can be as high as 2000 PPM or more before patients begin to complain of symptoms (nothing permanent...
...but you might be yawning a lot and begin to feel a little uncomfortable or queasy). Even in the presence of high levels of buffer, excessive CO2 can make a system have issues with chronically low pH. In many systems, the first thing to consider is that there is measurement error, often seen in probe use if the probe has not been recently cleaned and/or recalibrated. This can be tested by making the borax test solution up and seeing how your probe responds to this solution.
The issue becomes that your tank begins to act as an accumulating sink for CO2, and may just be an issue with high atmospheric CO2 in your home due to being closed up as already mentioned above for the winter. If you have adequate alkalinity, and your pH probe has passed the borax test (so we make sure that the issue is not a measurement error in the probe; this can occur even with a calibrated probe, sp do the borax test), the accumulation of CO2 has a measurable effect, as shown in the chart below.
This is a chart for the CO2 concentration determination based on what the actual measured pH via probe of the water column is and the corresponding alkalinity:
Ratio pCO2 For ASW compared to NSW
VALUE IN CHART IS COMPARED TO A VALUE OF 1 FOR nsw AT SEALEVEL, OR x:1
Total Alkalinity (AT)
(mEq/l) . . . 2.0 .. 2.5 .. 2.6 .. 3.0 .. 3.5 .. 4.0 .. 4.5 .. 5.0 ... 5.5 ... 6.0
(dKH) . . . . 5.6 .. 7.0 .. 7.3 .. 8.4 .. 9.8 . 11.2 . 12.4 . 14.0 . 15.4 . 16.8
pH __________________________________________________ _________
7.7---------3.0 .. 3.7 .. 3.9 .. 4.5 .. 5.3 .. 6.0 .. 6.8 ... 7.5 ... 8.3 ... 9.1
7.8---------2.3 .. 2.9 .. 3.0 .. 3.5 .. 4.1 .. 4.7 .. 5.3 ... 5.8 ... 6.4 ... 7.O
7.9---------1.8 .. 2.2 .. 2.3 .. 2.7 .. 3.1 .. 3.6 .. 4.0 ... 4.5 ... 5.0 ... 5.4
8.0---------1.3 .. 1.7 .. 1.8 .. 2.0 .. 2.4 .. 2.7 .. 3.1 ... 3.4 ... 3.8 ... 4.1
8.1---------1.0 .. 1.3 .. 1.3 .. 1.6 .. 1.8 .. 2.1 .. 2.3 ... 2.6 ... 2.9 ... 3.1
8.2---------0.8 .. 1.0 .. 1.0 .. 1.2 .. 1.4 .. 1.7 .. 1.8 ... 2.0 ... 2.2 ... 2.4
8.3---------0.6 .. 0.7 .. 0.7 .. 0.7 .. 1.0 .. 1.2 .. 1.3 ... 1.5 ... 1.6 ... 1.8
8.4---------0.4 .. 0.5 .. 0.5 .. O.6 .. 0.7 .. 0.9 .. 1.0 ... 1.1 ... 1.2 ... 1.3
8.5---------0.3 .. O.4 .. 0.4 .. 0.5 .. 0.5 .. 0.6 .. 0.7 ... 0.8 ... 0.9 ... 0.9
8.6---------0.2 .. 0.3 .. 0.3 .. 0.3 .. 0.4 .. 0.4 .. 0.5 ... 0.6 ... 0.6 ... 0.7
__________________________________________________ _________
Once the total alkalinity and pH are known, the ratio between the partial pressure of CO2 due to the atmosphere on seawater and the actual dissolved C02 of the system being evaluated can be determined utilizing the above chart. With the value from the chart known, you can decide whether you need to start ventilating the tank with outside air to your skimmer (or fans to the surface or remove glass tops if your tank uses them) to degas the CO2 content or if you need to increase your alkalinity.
For example, if your system's pH is 7.8 and your alkalinity was 2.6 mEq (7.3 dKH), then the value from the chart for the amount of CO2 dissolved in the water at normal atmospheric conditions is 3.0, so your pCO2 for the tank would be 3 times what it should be for normal concentrations of CO2 in your tank due to atmospheric dissolution of CO2 in the water COMPARED TO NSW (REMEMBER, many of us run higher than NSW values for Ca and alkalinity). If later in this same tank our pH were to be 8.2 but our akalinity were 2.6 mEq (7.3 dKH mEq/l), we would know that our pH was just about right and the amount of dissolved CO2 in the water column (pCO2) would be appropriate for the conditions present in the system.
If our chart lists a value of 3.0, or 3 times the amount of dissolved CO2 in our tank water compared to NSW, we would need to make arrangements to degas the tank for CO2 (and check our delivery rate of CO2 for systems equipped with CO2-based Ca reactors). For aquaria with CO2 reactors, if they are using a pH controller, we would prolly need to first check the calibration of the controller probe AND the tank probe, then test a second time for alkalinity.
It would be smart to do the mason jar test first, then make correctiions based on checking your pH testing methodology (pH probe tet with borax solution, there are plenty of threads here on how to perform this test). Post back and tell us how it goes with your evaluation of the system.
HTH!
меня зовут Chris 
He very well could explain it in a way easier to understand for most, but it amuses him that most of it still goes over our heads even when he spells it out for us
It looks my my geek rating just went up a point! 
