Sodium Bisulfate to Reduce Alkalinity in New Salt Water or in Display Tanks

[BCSreef]

I think the Seachem acid buffer has actual buffers in addition to bisulfate.

I recently mixed two 50 gallon batches of IO. I used HCl to lower alkalinity to ~7 dKH, aerated over night and pH was ~8.2.

Two weeks later I did the same but used 3 teaspoons of Seachem acid buffer to lower the IO to ~7 dKH. Aerated for 1, 2, then 3 days and each day, pH was at ~7.7.

 

[Randy Holmes-Farley]

I think the Seachem acid buffer has actual buffers in addition to bisulfate.

I recently mixed two 50 gallon batches of IO. I used HCl to lower alkalinity to ~7 dKH, aerated over night and pH was ~8.2.

Two weeks later I did the same but used 3 teaspoons of Seachem acid buffer to lower the IO to ~7 dKH. Aerated for 1, 2, then 3 days and each day, pH was at ~7.7.

I’m not convinced that’s the case. It couldn’t be a bicarbonate type of buffer.

 

[drawman]

Just tried this for the first time tonight and I will say it worked great at reducing alkalinity. I am going to let the water aerate overnight before I use it to get the pH back up since I'm not measuring it in my NSW for water changes.

 

[chipmunkofdoom2]

Sodium bisulfate is NaHSO4.

In seawater, it releases H+:

NaHSO4 ---> Na+ + H+ + SO4--

The H+ is what reduces the alkalinity, and the Na+ and SO4-- are not any concern:

H+ + CO3-- --> HCO3-

Hey @Randy Holmes-Farley, I'm having trouble understanding this. Could you clarify how the H+ reduces alkalinity? The second equation here looks like the forming of bicarbonate using carbonate and H+. I was under the impression that you'd actually need to convert bicarbonate into carbonic acid to reduce alkalinity, something like this:

HCO3- + H+ --> H2CO3

EDIT: Also, out of curiosity, could you also explain the part of the reaction that creates excess CO2? Thanks!

 

[Reefahholic]

Just tried this for the first time tonight and I will say it worked great at reducing alkalinity. I am going to let the water aerate overnight before I use it to get the pH back up since I'm not measuring it in my NSW for water changes.

How long did it take to get the pH in check??
You still using it. I’m thinking about switching over to this.

 

[drawman]

How long did it take to get the pH in check??
You still using it. I’m thinking about switching over to this.

I never made an attempt to measure pH but I let it aerate for about 16-24 hours. It has worked great for me and I haven't noticed any issues corals all respond well to water changes.

 

[Reefahholic]

Sounds great! Thx!

 

[Reefahholic]

While I would not suggest that you accept everything Seachem claims, and certainly not what others post to their web site, Seachem gives a value:

https://www.seachem.com/support/forums/forum/sunken-gardens/244-adding-seachem-acid-buffer-every-day

"Acid Buffer at a dose of 1/4 teaspoon per 20 gallons will lower your dKH by 0.6 points."

1/4 tsp drops the Alk anywhere from about 0.28 to 0.40 dKH in 35-44 gallons. If you make sure your tsp is very level, you’ll obviously see much more consistent numbers. I use it every few weeks and it works well. Drives your pH down, but I keep 2 air-stones in the brute. I can usually blow it all off within a few hours with the pump on and lid off. I would suggest to anybody using acid to drop pH to wait at least 12-24 hours before doing the water change. Less impact on your pH. If you’re only changing 5-10 gallons it’s not a big deal. If you’re changing 50% or more...I would wait.

 

[Randy Holmes-Farley]

Hey @Randy Holmes-Farley, I'm having trouble understanding this. Could you clarify how the H+ reduces alkalinity? The second equation here looks like the forming of bicarbonate using carbonate and H+. I was under the impression that you'd actually need to convert bicarbonate into carbonic acid to reduce alkalinity, something like this:

HCO3- + H+ --> H2CO3

EDIT: Also, out of curiosity, could you also explain the part of the reaction that creates excess CO2? Thanks!

missed this old post.

yes, you have it correct, and the carbonic acid is not stable. Most of it becomes CO2 and water:

H2CO3 —> H2O + CO2

 

[Randy Holmes-Farley]

1 tsp drops the Alk anywhere from about 0.28 to 0.40 dKH in my experience. If you make sure your tsp is very level, you’ll obviously see much more consistent numbers. I use it every few weeks and it works well. Drives your pH down, but I keep 2 air-stones in the brute. I can usually blow it all off within a few hours with the pump on and lid off. I would suggest to anybody using acid to drop pH to wait at least 12-24 hours before doing the water change. Less impact on your pH. If you’re only changing 5-10 gallons it’s not a big deal. If you’re changing 50% or more...I would wait.

Thanks for the update!

 

[Reefahholic]

Thanks for the update!

Thanks for the update!

Randy, I meant to say 1/4 tsp. I’ll go back and edit it. Here’s some of my notes of dropping the DKH with the Seachem Acid Buffer in 44/G brute. There was typically about 35-40 gallons in the brute. The dKH was dropped to match my tank dKH at that particular time.
———————————————
8.4 dKH
Dosed (2) 1/4 tsp Acid Buffer)
Result = 7.72 dKH.
[0.34 per 1/4 tsp Acid Buffer]
_____________________________________
9.40 dKH.
Dosed (6) 1/4 tsp Acid Buffer
Result = 7.67 dKH.
[0.28 per 1/4 tsp Acid Buffer]
———————————————
8.62 dKH.
Dosed (2) 1/4 tsp Acid Buffer
Result = 7.84 dKH.
[0.39 per 1/4 tsp Acid Buffer]
——————————————
9.29 dKH.
Dosed (4) 1/4 tsp of Acid Buffer
Result = 7.67 dKH.
[0.40 per 1/4 tsp of Acid Buffer]
——————————————
44/G Brute about 90% full
10.02 dKH
Dosed (4) level 1/4 tsp Acid Buffer
Result = 8.84 dKH.
[0.30 per 1/4 tsp Acid Buffer]
——————————————-

 

[pasquale petrovia]

Randy, My ALK is 12.5 and the lowest point before water change is 11.5. I use Reef crystals. 200 gallons of system water. Can I dose my 30 gallons per week of RODI makeup to lower it slowly between changes? Just a thought. If I aerate the fresh water 24 hours prior to dripping slowly into my sump or should I send it through my Kalk reactor like I currently do.

 

[Randy Holmes-Farley]

Randy, My ALK is 12.5 and the lowest point before water change is 11.5. I use Reef crystals. 200 gallons of system water. Can I dose my 30 gallons per week of RODI makeup to lower it slowly between changes? Just a thought. If I aerate the fresh water 24 hours prior to dripping slowly into my sump or should I send it through my Kalk reactor like I currently do.

the fresh water won’t benefit from aeration.The CO2 isn’t made until the acid encounters the alkalinity.
You might be able to just slowly add it in an ato, but a better bet would be to treat the new salt water and get it as low as you want before use in water changes.

 

[Bam327]

Randy, any idea of what I am doing wrong here? I'm trying to lower the alk of my new salt water (for a water change) and I'm following your directions with this except its barely working. I have ~32 gallons of water that started with an dKH of 11.7. I added 1.5 tsp of Sodium Bisulfate (I bought the exact stuff you linked to amazon) and it brought me down to 11.1 over 24 hours. I thought that was strange so I added 3 tsp of slurried Sodium Bisulfate and it only brough me to 10.4. I just added 2 TBSP more and am going to wait to see what happens. It just seems like way too much. I'm heating my water, have an airstone and a pump in it. My pH this morning before the 2 tbsp was 8.35. My target dKh is 9. I've decided its going to be easier to change salts moving forward, but I'd like to use what I have first.
Also, after adding the Sodium Bisulfate, how long should it take to go into affect? Thanks.

 

[Randy Holmes-Farley]

The effect of adding sodium bisulfate on alk is instantaneous. How are you measuring alkalinity?

You are using the Loudwolf material? Are you certain it says bisulfate?

 

[Bam327]

Ugh. I was so concerned with not buying bisulfite that I didn’t know this was sulfate or Na2SO4 instead of bisulfate. I’m assuming I just ruined 32 gallons of fresh salt water by adding this?

 

[Randy Holmes-Farley]

Ugh. I was so concerned with not buying bisulfite that I didn’t know this was sulfate or Na2SO4 instead of bisulfate. I’m assuming I just ruined 32 gallons of fresh salt water by adding this?

Sodium sulfate? That's no concern. Both sodium and sulfate are super high in seawater to begin with.

 

[Jeff Hollabaugh]

I just want to record these calculations in their own thread to refer back to in other threads.

When alkalinity is too high in new salt water or in a display tank, acid can be used to lower the alkalinity. You can easily use muriatic acid (hydrochloric acid), or sodium bifulfate (e.g., Seachem Acid Buffer is this chemical, I think) or sulfuric acid (but that one is harder to get for hobbyists).

Note that these methods reduce pH a lot (and to the same extent), until you aerate adequately, so go very slow in a display and aerate a lot to drive off the excess CO2 that is generated.

Dropping alk by 1.4 dKH when starting at 6.3 dKH will drop pH below 7 (I got 6.9, experimentally). The effect is roughly linear with alkalinity, so starting at 12.6 dKH, a drop of 2.8 dKH will drop the pH to around 7 or a bit lower (depends on the starting pH, of course).

Sodium bisulfate is NaHSO4.

In seawater, it releases H+:

NaHSO4 ---> Na+ + H+ + SO4--

The H+ is what reduces the alkalinity, and the Na+ and SO4-- are not any concern:

H+ + CO3-- --> HCO3-

So, how much is needed?

NaHSO4 weighs 120.1 grams per mole. Thus, 120.1 grams has the potential to reduce alkalinity by 1 mole, or 1 equivalent, or 1000 meq (milliequivalents).

If you were to add that much to 1000 L, you would drop the alkalinity by 1000 meq/1000L = 1 meq/L = 2.8 dKH.

So 1.2 grams per 10 Liters, drops alkalinity by 2.8 dKH.

If you do not have a scale, we can roughly estimate how much is in a teaspoon:

1 cubic centimeter (1 mL dry) weighs roughly 1.44 grams.

A level teaspoon (4.93 mL) will then weigh roughly 7.1 grams.

1 level dry teaspoon of sodium bisulfate added per 100 L of tank water will drop the alkalinity by about 1.7 dKH.

Dissolve it in fresh water before adding it slowly to a high flow area.

DO NOT USE BISULFITE. Note the "i" in the ending vs an "a"

These materials should be fine to use:

Hi I am having this problem and am going to try using the product you recommended will this stabilize my alk in the long term, just curious

 

[Randy Holmes-Farley]

Hi I am having this problem and am going to try using the product you recommended will this stabilize my alk in the long term, just curious

It lowers alkalinity. I'm not sure what you mean by stabilize alkalinity.

What is happening to your alkalinity without it?

 

[Jeff Hollabaugh]

I just want to record these calculations in their own thread to refer back to in other threads.

When alkalinity is too high in new salt water or in a display tank, acid can be used to lower the alkalinity. You can easily use muriatic acid (hydrochloric acid), or sodium bifulfate (e.g., Seachem Acid Buffer is this chemical, I think) or sulfuric acid (but that one is harder to get for hobbyists).

Note that these methods reduce pH a lot (and to the same extent), until you aerate adequately, so go very slow in a display and aerate a lot to drive off the excess CO2 that is generated.

Dropping alk by 1.4 dKH when starting at 6.3 dKH will drop pH below 7 (I got 6.9, experimentally). The effect is roughly linear with alkalinity, so starting at 12.6 dKH, a drop of 2.8 dKH will drop the pH to around 7 or a bit lower (depends on the starting pH, of course).

Sodium bisulfate is NaHSO4.

In seawater, it releases H+:

NaHSO4 ---> Na+ + H+ + SO4--

The H+ is what reduces the alkalinity, and the Na+ and SO4-- are not any concern:

H+ + CO3-- --> HCO3-

So, how much is needed?

NaHSO4 weighs 120.1 grams per mole. Thus, 120.1 grams has the potential to reduce alkalinity by 1 mole, or 1 equivalent, or 1000 meq (milliequivalents).

If you were to add that much to 1000 L, you would drop the alkalinity by 1000 meq/1000L = 1 meq/L = 2.8 dKH.

So 1.2 grams per 10 Liters, drops alkalinity by 2.8 dKH.

If you do not have a scale, we can roughly estimate how much is in a teaspoon:

1 cubic centimeter (1 mL dry) weighs roughly 1.44 grams.

A level teaspoon (4.93 mL) will then weigh roughly 7.1 grams.

1 level dry teaspoon of sodium bisulfate added per 100 L of tank water will drop the alkalinity by about 1.7 dKH.

Dissolve it in fresh water before adding it slowly to a high flow area.

DO NOT USE BISULFITE. Note the "i" in the ending vs an "a"

These materials should be fine to use:

Just ordered some and am gonna give it a try