Using a Controller to Maintain Alkalinity and Calcium Levels (and Mg and pH?)

[Dr. Jim]

I’m starting to make plans for using a GHL Controller to regulate Alk and Ca levels (as well as Mg and possibly pH). Before going too far with my programming, I want to make sure that I am not missing any key concepts or details, so I’d like to present my plans and see if anyone sees any flaws in my design, from the standpoint of chemistry (@Randy Holmes-Farley) as well as practicality. If any of the statements I make throughout the presentation are not accurate, please chime in. It is important to note that I am using a relatively “young” (4 mo old) 40 gal cube for SPS only and, at the moment, have about 30 small frags. (A mature, heavily loaded tank may require a modification as explained in the next paragraph).

I am currently using pH to control Kalk vs “non-Kalk" ATO additions. I believe I read in one of the threads that it is better to use pH as a control of Kalk vs “non-kalk", but I’ve come to the conclusion that it might be better to use Alkalinity to control these additions (at least in a relatively new tank with little SPS mass. This is because the almost constant use of Kalk in the ATO water (to raise pH) raises the alkalinity too high because of the relatively little alkalinity “usage” compared to a heavily loaded SPS tank. (In my former 200 gal tank, loaded with SPS colonies, constant use of kalk in the ATO water wasn’t enough to keep adequate Alk levels and other buffers were needed so perhaps pH could be used in a “mature” system). Can it be agreed that it is best to use Alk rather than pH to control Kalk additions in a “new” tank (that isn’t “using” much Alk)?

I will start with a balanced ratio of Alk = 8.0 and Ca = 420 with the goal of maintaining these levels. (Mg and pH will be discussed later). I will use the following solutions:
-Triton 4-Part (must be dosed in equal portions)
-Kalkwasser (Kalk)
-Buffer
-CaCl
-Mg solution

The Controller will be programmed as follows to regulate additions of these solutions:

A) I will first set the dosing for the 4 Triton parts so the “Limiting Part” (Alk, Ca or Mg) will not rise above its desired level. (“Limiting Part” = whichever parameter reaches its desired level first).
-- If both Ca and Alk are low, then Kalk will be added until either Ca or Alk reaches its desired level
-- If Ca is at desired level (420) but Alk is low, then Buffer will be added
-- If Alk is at desired level (8.0) but Ca is low, then CaCl will be added.

B) On a separate control, if Mg is low AFTER Ca and ALK are at desired levels, then Mg will be added.

C) pH: It would be nice to maintain the pH at the highest and most stable level (not to exceed 8.3) if possible. Which would be better for SPS growth (using theoretical examples, assuming that best growth is at 8.3):
-- a pH ranging from 8.1-8.3 (with a 0.2 daily swing), or
-- a more STABLE and constant pH of 8.15 (and thereby sacrificing the benefits of 8.3 at least during part of the day) (@Lasse?)

The only way I can think of controlling pH, at the moment, is by using a solenoid to control CO2 scrubbing. (@Lasse?) (I will work on this step after mastering the first two….hopefully!)

Although not relative to this discussion, I will mention that I am a huge fan of Zeovit additives (at a fraction of the recommended dosages for many of them) and will use ICP testing to regulate them (and trace elements in general). N-DOC testing will also be implemented.

Also, a GHL kH Director (for Alk readings multiple times a day) is being used and I have the ION Director coming for Ca, Mg (and other parameters.)

If anyone sees any flaws in any of my “thinking” and/or can make any suggestions, your comments will be most appreciated! Thank you.

 

[Randy Holmes-Farley]

It may be possible to shift from hydroxide to carbonate or bicarbonate alk supplements to control pH, but it also may not be since some folks using all hydroxide still do not have pH at 8.3 (stays lower).

i might use sodium hydroxide of equal potency to the sodium carbonate or bicarbonate to simplify the things being varied.

Magnesium demand will be very low. "Control" seems unecessary, IMO, and maybe problematic as the daily demand will be much lower than testing errors.

 

[Dr. Jim]

It may be possible to shift from hydroxide to carbonate or bicarbonate alk supplements to control pH, but it also may not be since some folks using all hydroxide still do not have pH at 8.3 (stays lower).

i might use sodium hydroxide of equal potency to the sodium carbonate or bicarbonate to simplify the things being varied.

Magnesium demand will be very low. "Control" seems unecessary, IMO, and maybe problematic as the daily demand will be much lower than testing errors.

Yes, my pH never gets near 8.3 with kalk.

Are you saying that sodium hydroxide will raise the pH more than the Kalk will?

Is there an easy way to determine the amount of sodium hydroxide to add to sodium carbonate or bicarbonate to give "equal potency."

Is there a recommended ration of sodium carbonate to sodium bicarbonate that would be good to use to raise the pH?

Thank you!

 

[Randy Holmes-Farley]

Yes, my pH never gets near 8.3 with kalk.

Are you saying that sodium hydroxide will raise the pH more than the Kalk will?

Is there an easy way to determine the amount of sodium hydroxide to add to sodium carbonate or bicarbonate to give "equal potency."

Is there a recommended ration of sodium carbonate to sodium bicarbonate that would be good to use to raise the pH?

Thank you!

Hydroxide has the same pH effect whatever chemical is dosed (assuming it dissolves). But you could have equi-potent sodium hydroxide and sodium bicarbonate and you just switch between the two by controller. You cannot do that as easily with the much less potent calcium hydroxide. Maybe equal potency is unimportant, but it would seem simpler.

If the goal is only to raise pH, I wouldn't use any bicarbonate, just carbonate or hydroxide.

 

[Dr. Jim]

Hydroxide has the same pH effect whatever chemical is dosed (assuming it dissolves). But you could have equi-potent sodium hydroxide and sodium bicarbonate and you just switch between the two by controller. You cannot do that as easily with the much less potent calcium hydroxide. Maybe equal potency is unimportant, but it would seem simpler.

If the goal is only to raise pH, I wouldn't use any bicarbonate, just carbonate or hydroxide.

So just to be sure I understand....

-Calcium hydroxide vs sodium hydroxide (when fully saturated?):
a) will raise pH equally, but sodium hydroxide has a greater effect on alkalinity than calcium hydroxide?
b) both have less of an effect on alkalinity than bicarbonate? (or can sodium hydroxide's effect be equal to bicarbonate's effect on alkalinity)?

-Hydroxide vs carbonate:
a) Which has the greater effect on alkalinity?
b) Which has the greater effect on pH?


Thanks again!

 

[Randy Holmes-Farley]

So just to be sure I understand....

-Calcium hydroxide vs sodium hydroxide (when fully saturated?):
a) will raise pH equally, but sodium hydroxide has a greater effect on alkalinity than calcium hydroxide?
b) both have less of an effect on alkalinity than bicarbonate? (or can sodium hydroxide's effect be equal to bicarbonate's effect on alkalinity)?

-Hydroxide vs carbonate:
a) Which has the greater effect on alkalinity?
b) Which has the greater effect on pH?


Thanks again!

No.

For each hydroxide ion added, sodium hydroxide and calcium hydroxide have exactly the same effect on both pH and alkalinity. About 0.6-0.7 pH units per 1.4 dKH added (when added instantly).

Carbonate has a lower pH effect, about 0.35 pH units per 1.4 dKH added

Bicarbonate slightly lowers pH and adds alkalinity (less than 0.1 pH unit drop per 1.4 dKH added).

After full aeration, the pH of all of these will end up the same.

i show that here:

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH

Randy answers many questions in this complex relationship.

reefs.com

 

[Lasse]

C) pH: It would be nice to maintain the pH at the highest and most stable level (not to exceed 8.3) if possible. Which would be better for SPS growth (using theoretical examples, assuming that best growth is at 8.3):
-- a pH ranging from 8.1-8.3 (with a 0.2 daily swing), or
-- a more STABLE and constant pH of 8.15 (and thereby sacrificing the benefits of 8.3 at least during part of the day) (@Lasse?)

The only way I can think of controlling pH, at the moment, is by using a solenoid to control CO2 scrubbing. (@Lasse?) (I will work on this step after mastering the first two….hopefully!)

It is not enough to control CO2 scrubbing with a valve. I have done that. Had a three way valve that altered from scrubbed air to air from the cabinet depending on pH. It works well for setting the low point of pH but I got a pH raise when photosynthesis started.

however - in an experiment we set up - I controlled the pH very well (plus minus 0.01 in pH most time) with help of CO2 bubbling and aeration with CO2 free air (scrubbed). what I remember one of the pH we run was 8.3

Sincerely Lasse

 

[Dr. Jim]

No.

For each hydroxide ion added, sodium hydroxide and calcium hydroxide have exactly the same effect on both pH and alkalinity. About 0.6-0.7 pH units per 1.4 dKH added (when added instantly).

Carbonate has a lower pH effect, about 0.35 pH units per 1.4 dKH added

Bicarbonate slightly lowers pH and adds alkalinity (less than 0.1 pH unit drop per 1.4 dKH added).

After full aeration, the pH of all of these will end up the same.

i show that here:

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH

Randy answers many questions in this complex relationship.

reefs.com

Excellent article, Randy....thank you!

Now I understand that it almost doesn't matter which is used, hydroxide, carbonate or bicarbonate, because the end result is the same (i.e. each will produce the same pH for a given resulting alkalinity).

But then, I have to wonder:

1) Why you wrote: …. "to use sodium hydroxide instead of calcium hydroxide" ….and ...….."you could have equi-potent sodium hydroxide and sodium bicarbonate and you just switch between the two by controller." What is each one doing differently and how would they be used in my situation using a controller?

2) Why you wrote: "If the goal is only to raise pH, I wouldn't use any bicarbonate, just carbonate or hydroxide" Why would it matter which one is used since they all end up at the same pH anyway (although at different rates)?

3) Why is kalkwasser even considered since the end result (pH; alk) is the same no matter which is used and the kalkwasser has the disadvantage of the initial pH spike?

One of my initial goals was to find which "buffer" will raise pH with minimal effect on alkalinity but I now see that using "buffers" is not the way to raise pH (if the Alk is where you want it already). Other methods, such as CO2 control, are necessary.

I also think that all this confirms that, with a Controller, alkalinity should control "buffer" additions, not pH, (otherwise, alkalinity can potentially rise to unwanted high levels).