I think i made a boo boo

[DevilBoy]

My pH was reading low, so i dosed with some baking soda. I checked my alk today and it tested at 12.6 dKH . Which is too high for my liking, but my pH now is at 8.19

I read earlier today that the salt mix i use will measure at 11dKH with a salinity of 1.026.

[jennmac415]

what salt do you use?

[jennmac415]

doesn't straight baking soda without baking it lower the PH?

[DevilBoy]

im using Tropic Marin

[tdwyatt]

Originally Posted by jennmac415

doesn't straight baking soda without baking it lower the PH?

pKa of sodium bicarbonate is around 8.2. There is an initial drop in pH when adding the solution (you DO dissolve the powder in about 2 or 3 liters of ro/di before adding it, don't you? )
due to the release of CO2 (the most rapid part of the reaction equilibrium), but once the entire list of species come to equilibrium (CO2<--->HCOOH <--->H+ + COOH <---> HCO3- <---> CO3-- <---> (usually calcium salt)CaCO3 _solid ), the pH of the solution (remember that 90% of seawater alkalinity is due to the presence of bicarbonate as the predominant inorganic carbon ion specie) will center around the dissociation constant @ STP for bicarbonate, or a pH of 8.2: just happens to be that of NSW...

There really is no reason to "cook" baking soda to get a perfectly good alk supplement, just make sure to add it slowly AFTER DISSOLVING IT IN WATER. Keep in mind that you are adding SODIUM bicarbonate, and the corals do not use sodium to make their skeletons. If you are in a hurry, adding about 1/8 W/W sodium carbonate (the result of baking baking soda at about 200 to 250 ^o F for 30 to 60 minutes) to your bicarb will keep it from the initial pH drop (pKa of Na2CO3 is ~11.4 I think) and the final equilibrium will be reached more quickly due to the presence of the right amount of carbonate specie.


HTH

[DevilBoy]

Originally Posted by tdwyatt

pKa of sodium bicarbonate is around 8.2. There is an initial drop in pH when adding the solution (you DO dissolve the powder in about 2 or 3 liters of ro/di before adding it, don't you? )
due to the release of CO2 (the most rapid part of the reaction equilibrium), but once the entire list of species come to equilibrium (CO2<--->HCOOH <--->H+ + COOH <---> HCO3- <---> CO3-- <---> (usually calcium salt)CaCO3 _solid ), the pH of the solution (remember that 90% of seawater alkalinity is due to the presence of bicarbonate as the predominant inorganic carbon ion specie) will center around the dissociation constant @ STP for bicarbonate, or a pH of 8.2: just happens to be that of NSW...

There really is no reason to "cook" baking soda to get a perfectly good alk supplement, just make sure to add it slowly AFTER DISSOLVING IT IN WATER. Keep in mind that you are adding SODIUM bicarbonate, and the corals do not use sodium to make their skeletons. If you are in a hurry, adding about 1/8 W/W sodium carbonate (the result of baking baking soda at about 200 to 250 ^o F for 30 to 60 minutes) to your bicarb will keep it from the initial pH drop (pKa of Na2CO3 is ~11.4 I think) and the final equilibrium will be reached more quickly due to the presence of the right amount of carbonate specie.


HTH

Well may this will explain why i had a pH drop and now its back up. but what about my high dKH reading

[tdwyatt]

btw, it usually only takes an hour or so to come to equilibrim after adding bicarb to a ASW tank, check your pH after 60 minutes to see the results. Unless there are large amounts of organic acids or you have a sandbed that has been dumping protons into the water column, you should have good alkalinity levels and a pH of around 8.2 or so, depending on what part/time of day and the number of photoseynthetic organisms (macroalgae in particular) you have in the system.

HTH

[tdwyatt]

Originally Posted by DevilBoy

Well may this will explain why i had a pH drop and now its back up. but what about my high dKH reading

You are adding dKH when you add bicarbonate to the system, expect this to happen. If you need to drop dKH, don't add bicarb, or add some calcium chloride to drop the level of alk in the system. Keep in mind that you'll be adding CaCL2, and that the coral will only use the Ca++ to make skeletons, leaving the Cl2 behind...

sodium from the bicarb, plus chloride from the calium chloride, makes...


????????

[DevilBoy]

i have no idea you got me lost Tom... i know why now the reason i hated chemistry

[DevilBoy]

if i drop the alk then wont the pH also drop with it?

[Geoff]

pH and alk are not the same. pH is mainly controlled by the CO2 levels in the tank. if you have very high CO2 levels in the tank then you will always have a low pH. the amount of alk will keep it from swinging excessively.

G~

[betamed]

SALT

sodium from the bicarb, plus chloride from the calium chloride, makes...


????????


[/quote]

[tdwyatt]

Originally Posted by betmed

SALT

YOU ARE CORRREEEECCCTTTT, SIR!!!!


I point this out to remind folks of the big disadvantage of using any 2 part supplement in a reef system. These products are relatively easy to use, and do a great job in correcting calcium and alkalinity, and they are easy to calculaste in terms of fixing the tank. The excess NaCl you form when supplementing or correcting your hermatypic additives will drive up significantly your SG for the tank water. To correct this, you most often will take out a scoop of tank water and replace it with RO/DI to drop your salinity/SG. The scoop of tank water will pull not only the excess sodium and chloride, but the normal amounts of potassium, magnesium, calcium, sulfate, bicarbonate, etc. that are conservative elements in seawater, reducing their effective amounts in the makeup of your ASW. Each time you do this correction, you increase the proportiion of sodium and chloride, and reduce the remaining percentages of the other conservative elements, until you eventually end up with a sodium chloride brine rather than seawater. If you do not try to correct what will appear as a reduction of Mg in the seawater (remember, there really are few if any spp of organisms that use magnesium in significant amounts, only some unusual corallinaceae and an incidental inclusion in some skeletal development (rare), then you can measure how significant an issue this is in your system by what your Mg++ values are when the tank is at 35 PPT salinity @80^oF. If your Mg is 1100 PPM and you know that IO is supposed to be Mg=1250 PPM Mg when S=35 @80^oF, then you know that there is a shift loss of conservative proportionality of 1100/1250, almost 88% of what it should be.


This is easily corrected without doing a Mg supplementation, rather just do water changes to bring up the percentages of ALL your values, including calcium and alkalinity to NSW values...