Alk question driving me nuts

[Randy Holmes-Farley Verified Community Expert]

Do you have a refugium? Photosynthesis in macros and some corals consumes bicarbonate as a CO2 source. My tank only has macroalgae and a couple of soft corals and I have to dose a lot of alkalinity daily

Yes and no.

Macroalgae may take in bicarbonate as a CO2 source, but they do not deplete alkalinity because when using bicarbonate, they MUST spit back out OH-, keeping the alk in the water unchanged.

HCO3- ---> CO2 + OH-

 

[Randy Holmes-Farley Verified Community Expert]

I have found much the same thing when trying to dose these two and three-part systems in smaller tanks. I found much better success when I switched to an all in one balanced solution. Kalkwasser then carbo-calcium , All-for-reef (which is the same thing with trace) and now I use a calcium reactor. All produced much more stable and better results for me than two-part. I cannot believe how stable my tank is with a calcium reactor. It is the only way I will ever run a reef tank from now on.

I don't think this makes general chemical sense, but there's nothing wrong with using those other systems if you like them. Your experience may have related to how and what you dosed, not the method itself.

 

[Andy Macro]

Yes and no.

Macroalgae may take in bicarbonate as a CO2 source, but they do not deplete alkalinity because when using bicarbonate, they MUST spit back out OH-, keeping the alk in the water unchanged.

HCO3- ---> CO2 + OH-

Yes, pH goes up during this process. I counter this a bit by adding ammonium with my daily dose.

 

[Randy Holmes-Farley Verified Community Expert]

Yes, pH goes up during this process. I counter this a bit by adding ammonium with my daily dose.

But my point was not the pH boost, but the alkalinity remaining unchanged.

 

[Andy Macro]

But my point was not the pH boost, but the alkalinity remaining unchanged.

I'm confused now. Here is what I see:

HCO3 - ---> CO2 (macro eats it) + OH- (ph rise)

this means HCO3 goes down and therefore buffering capacity of water goes down.
I measure a drop of 1.5 dKH if I don't add anything to the tank. With the current Allforreef I'm dosing Calcium is stable but I still need to add 1 dKH equivalent of bicarbonate daily

 

[MA Reefer]

Do you have a refugium? Photosynthesis in macros and some corals consumes bicarbonate as a CO2 source. My tank only has macroalgae and a couple of soft corals and I have to dose a lot of alkalinity daily

Fuge- sand bottom, few lbs of rubble, and chaeto with 100w led grow fixture

 

[MA Reefer]

Always refer to dosing issues in dKH per day. mL per day just forces people do get out a calculator and determine if you are dosing an appropriate amount for your size tank or not.

Is the 2 cups measured before or after baking?

Assuming you made my DIY Recipe 1 correctly, then you are dosing 3.4 dKH per day. That is quite a bit. Perhaps not necessarily too much, but its on the high end.


I would back off on the alkalinity (maintaining ~7 dKH), and switch to the unbaked version to lower pH, and see what effect that has on demand.

Dose to a very high flow area, and possibly more slowly.

If that substantially lowers the demand but corals seem OK, then we can go from there.

2 cups measure AFTER baking

Was thinking by letting the co2 scrubber go....didn't seem like it was doing alot, but might be the api test kit....if i was running a little acidic but not detectable maybe the extra H+ ions were being absorbed by the carbonate and using it up?

Im rusty with my inorganic chemistry

If high 7 low 8s is an ok "stable" range maybe the answer is to stop messing with it and not worry so much about 7s....guess i was worrying about the commonly discussed 8-10 "ideal" range

Great thread im learning a lot

 

[Andy Macro]

Fuge- sand bottom, few lbs of rubble, and chaeto with 100w led grow fixture

Perhaps it's that, the chaeto is doing too well

 

[Randy Holmes-Farley Verified Community Expert]

I'm confused now. Here is what I see:

HCO3 - ---> CO2 (macro eats it) + OH- (ph rise)

this means HCO3 goes down and therefore buffering capacity of water goes down.
I measure a drop of 1.5 dKH if I don't add anything to the tank. With the current Allforreef I'm dosing Calcium is stable but I still need to add 1 dKH equivalent of bicarbonate daily

That is not a correct interpretation. There must be zero consumption of alkalinity by any macroalgae that is not depositing calcium carbonate (e.g., Halimeda deposits calcium carbonate and uses calcium and alk). There is just to way for ordinary macroalgae to use up or deposit alkalinity.

OH- is a perfectly suitable component of alkalinity even as added (shows on an alk kit, etc.), but when added, most of it combines with bicarbonate ions to form carbonate. Carbonate has twice the alkalinity of bicarbonate.

OH- + HCO3- --> CO3-- + H2O

All For Reef is a complicated product. TM does not recommend dosing it by alkalinity since it will not show on an alk kit, at least not until it is metabolized and released back as bicarbonate.

 

[Randy Holmes-Farley Verified Community Expert]

Perhaps it's that, the chaeto is doing too well

No, that is not a correct interpretation for an alkalinity issue. Please read up and understand the issue.

 

[Randy Holmes-Farley Verified Community Expert]

2 cups measure AFTER baking

Was thinking by letting the co2 scrubber go....didn't seem like it was doing alot, but might be the api test kit....if i was running a little acidic but not detectable maybe the extra H+ ions were being absorbed by the carbonate and using it up?

Im rusty with my inorganic chemistry

If high 7 low 8s is an ok "stable" range maybe the answer is to stop messing with it and not worry so much about 7s....guess i was worrying about the commonly discussed 8-10 "ideal" range

Great thread im learning a lot

OK, I'm not certain what volume should be used after baking, but that is probably reasonably close.

I'd drop the scrubber for now. Low pH is your friend if abiotic precipitation is a potential problem.

 

[Andy Macro]

That is not a correct interpretation. There must be zero consumption of alkalinity by any macroalgae that is not depositing calcium carbonate (e.g., Halimeda deposits calcium carbonate and uses calcium and alk). There is just to way for ordinary macroalgae to use up or deposit alkalinity.

OH- is a perfectly suitable component of alkalinity even as added (shows on an alk kit, etc.), but when added, most of it combines with bicarbonate ions to form carbonate. Carbonate has twice the alkalinity of bicarbonate.

OH- + HCO3- --> CO3-- + H2O

All For Reef is a complicated product. TM does not recommend dosing it by alkalinity since it will not show on an alk kit, at least not until it is metabolized and released back as bicarbonate.

Plants and macroalgae adapted to high alkalinity waters adapted to use carbonate as a way to obtain CO2 because CO2 is found in very small concentrations.

In the case of Macroalgae they do this by absorbing carbonate and transporting it to the spaces between their cells. In those "cell walls" they artificially decrease the pH by pumping H+ ions to that space. This forces the carbonate to turn to CO2 more easily which in turn they then pump in and use for photosynthesis. The net result of all of this is of course a -OH ion which the cells would release back to the water column.

The reason why most reefers don't spot this is because they are actively dosing carbonate for their hard corals and don't have a large macroalgae biomass to notice but if you have a mostly macroalgae tank like mine you will notice the effect quite strongly and will notice how the alkalinity consumed decreases with reduced light (less photosynthesis), more aeration (available CO2) , pruning , and less water flow.
Ask any macroalgae grower and you will get the same answer, macros won't grow unless you supplement alkalinity.

 

[Randy Holmes-Farley Verified Community Expert]

Plants and macroalgae adapted to high alkalinity waters adapted to use carbonate as a way to obtain CO2 because CO2 is found in very small concentrations.

In the case of Macroalgae they do this by absorbing carbonate and transporting it to the spaces between their cells. In those "cell walls" they artificially decrease the pH by pumping H+ ions to that space. This forces the carbonate to turn to CO2 more easily which in turn they then pump in and use for photosynthesis. The net result of all of this is of course a -OH ion which the cells would release back to the water column.

The reason why most reefers don't spot this is because they are actively dosing carbonate for their hard corals and don't have a large macroalgae biomass to notice but if you have a mostly macroalgae tank like mine you will notice the effect quite strongly and will notice how the alkalinity consumed decreases with reduced light (less photosynthesis), more aeration (available CO2) , pruning , and less water flow.
Ask any macroalgae grower and you will get the same answer, macros won't grow unless you supplement alkalinity.

Sorry, you are absolutely mistaken. Seriously, please stop repeating this until you get a better understanding of the process. You are grossly misleading people.

yes, many marine algae take up bicarbonate as a source of CO2. You can read that in my article on that specific process:

Photosynthesis and the Reef Aquarium, Part I: Carbon Sources by Randy Holmes-Farley - Reefkeeping.com

But to say it "consumes" alkalinity is seriously mistaken. You admit that OH- is released back to the water, and it carries the alkalinity back into the water. Hydroxide is alkalinity.

Thus, there is no net loss of alkalinity from the use of bicarbonate as a source of CO2. Hydroxide = alkalinity.

 

[Andy Macro]

Sorry, you are absolutely mistaken. Seriously, please stop repeating this until you get a better understanding of the process. You are grossly misleading people.

yes, many marine algae take up bicarbonate as a source of CO2. You can read that in my article on that specific process:

Photosynthesis and the Reef Aquarium, Part I: Carbon Sources by Randy Holmes-Farley - Reefkeeping.com

But to say it "consumes" alkalinity is seriously mistaken. You admit that OH- is released back to the water, and it carries the alkalinity back into the water. Hydroxide is alkalinity.

Thus, there is no net loss of alkalinity from the use of bicarbonate as a source of CO2. Hydroxide = alkalinity.

That's a great article.

I will replace "it consumes alkalinity" with "consumes bicarbonate".

I still have one doubt though, being -OH considered alkalinity why the tests kits show a decrease in alkalinity (API and Hannah)? Though I do have Halimeda growing now it it wasn't always the case and the ~1dKH decrease daily has been a constant.

 

[The Opinionated Reefer]

I don't think this makes general chemical sense, but there's nothing wrong with using those other systems if you like them. Your experience may have related to how and what you dosed, not the method itself.

yes, I think it was because I was dosing into a small tank with high consumption. It was just too hard to dial in the two-part well enough at the time. If i was to do it again i would heavily dilute the solutions and break the doses up more.

 

[MA Reefer]

OK, I'm not certain what volume should be used after baking, but that is probably reasonably close.

I'd drop the scrubber for now. Low pH is your friend if abiotic precipitation is a potential problem.

Many thanks- im going to take the scrubber off...maybe bump up the mix a bit. Looks like ur recipe is 2 1/4 cups bicarb....i only did 2 so i can probably push it a bit and see if i get participate.

Thanks for the advice we'll see where it goes.

 

[Randy Holmes-Farley Verified Community Expert]

That's a great article.

I will replace "it consumes alkalinity" with "consumes bicarbonate".

I still have one doubt though, being -OH considered alkalinity why the tests kits show a decrease in alkalinity (API and Hannah)? Though I do have Halimeda growing now it it wasn't always the case and the ~1dKH decrease daily has been a constant.

Almost all tanks have some abiotic precipitation of calcium carbonate, even if it is unseen. If the pH or alk are on the high side, that accelerates the process.

 

[Andy Macro]

Almost all tanks have some abiotic precipitation of calcium carbonate, even if it is unseen. If the pH or alk are on the high side, that accelerates the process.

That still does not explain why the dKH stops stopping when I turn of the light or prune the macros

 

[Randy Holmes-Farley Verified Community Expert]

That still does not explain why the dKH stops stopping when I turn of the light or prune the macros

Most alk demand in a reef tank, likely including abiotic precipitation, happens during the daytime, which is when pH is highest. It is not 100% clear if that effect in corals is a pH effect or a light effect, or both. I'm still waiting for a nice experiment where someone has a pH cycle offset from the coral light cycle. For abiotic precipitation, it would be the pH effect..

That pH effect would explain the lighting effect in your case. Maybe the pruning also reduces the peak pH from less photosynthesis.

 

[Andy Macro]

Most alk demand in a reef tank, likely including abiotic precipitation, happens during the daytime, which is when pH is highest. It is not 100% clear if that effect in corals is a pH effect or a light effect, or both. I'm still waiting for a nice experiment where someone has a pH cycle offset from the coral light cycle. For abiotic precipitation, it would be the pH effect..

That pH effect would explain the lighting effect in your case. Maybe the pruning also reduces the peak pH from less photosynthesis.

I checked the solubility of calcium hydroxide and it's pretty low so it would make sense if it's precipitating.