trouble with raising alk

[Spare time]

So I use brs soda ash and for some reason, no matter how much I dose (be that 60ml, 90, 120ml or whatever), my alk will never go above 8. Occasionally I can get to 9. I add it to my overflow. I have used the red sea pro alk test and the api one. However, when I used a small sample bottle of red sea alk supplement, my alk finally went up and I added it into the overflow just like the soda ash mix..

Any clue what is going on? I don't think I am dosing too much so I am not sure why it would be precipitating if that is the cause. Maybe the overflow doesn't have enough flow to stop precipitation?

 

[Copingwithpods]

What are your cal and mag sitting at?

 

[Old Reefer]

What are your cal and mag sitting at?

Thats what i was thinking. Cal is probably high and Mag is very low. Happened to me, Alk just wouldn't get right, because my Mag was so low, now they're all balanced .

 

[Greg P]

@Spare time what is your Mag test?
Mag will limit Alk and Ca levels

 

[Randy Holmes-Farley]

How soon after dosing are you measuring it?

120 mL corresponds to how much dKH in your aquarium?

 

[Spare time]

@Spare time what is your Mag test?
Mag will limit Alk and Ca levels

It was at 1400 last time I checked (around 2 weeks ago, but it doesn't drop very fast in my system).

 

[Spare time]

How soon after dosing are you measuring it?

120 mL corresponds to how much dKH in your aquarium?

I will dose in the morning and then test in the evening

around 36ml is supposed to raise it by 0.5KH in my tank (give or take a little due to error in estimating water without rocks).

I only dosed 120ml in one day twice and I spread it out in the morning and evening. However I just stop at 60ml as I seem to make no progress plus I don't want to swing the ph that much.

 

[Randy Holmes-Farley]

I will dose in the morning and then test in the evening

around 36ml is supposed to raise it by 0.5KH in my tank (give or take a little due to error in estimating water without rocks).

I only dosed 120ml in one day twice and I spread it out in the morning and evening. However I just stop at 60ml as I seem to make no progress plus I don't want to swing the ph that much.

That's why I asked: you really are not dosing huge amounts. 60 mL means less than 1 dKH per day. Even some soft coral tanks can use 2 dKH per day from coralline algae alone.

What is in the tank that might be using alk?

If you dose and do not measure until the evening, the tank may just be using it.

I might switch to baking soda for a while to let the pH drop back and reduce the potential for precipitation, but the consumption may be normal.

 

[Randy Holmes-Farley]

It was at 1400 last time I checked (around 2 weeks ago, but it doesn't drop very fast in my system).

It shouldn't. Real magnesium depletion is about 1/10th of the calcium depletion or less, and 0-2 ppm per day is about all you'd expect.

 

[Spare time]

That's why I asked: you really are not dosing huge amounts. 60 mL means less than 1 dKH per day. Even some soft coral tanks can use 2 dKH per day from coralline algae alone.

What is in the tank that might be using alk?

If you dose and do not measure until the evening, the tank may just be using it.

I might switch to baking soda for a while to let the pH drop back and reduce the potential for precipitation, but the consumption may be normal.

I have a mix of corals that are using it. I was just confused as for some reason my alk went up with the red sea alk additive and not the soda ash. Typically I can go through 1KH a day. I guess that maybe my corals are just experiencing a boost in growth and I need to adjust how much I am dosing. I am just confused as to why I am struggling to raise my alk higher than 8 when dosing what I thought was enough to go beyond 1KH. I like my alk to be at 10 or 11.

 

[Randy Holmes-Farley]

I have a mix of corals that are using it. I was just confused as for some reason my alk went up with the red sea alk additive and not the soda ash. Typically I can go through 1KH a day. I guess that maybe my corals are just experiencing a boost in growth and I need to adjust how much I am dosing. I am just confused as to why I am struggling to raise my alk higher than 8 when dosing what I thought was enough to go beyond 1KH. I like my alk to be at 10 or 11.

Lower pH alk additives may allow higher alk through lower tank pH or lower pH where first added.

 

[Spare time]

So I put in 120ml and I raised the alk by 0.6 (75 tank and sump is somewhere around 20 gal). Brs calculator is way lower then that which confuses me. I put another 60+ml in and it didn't go up at all from that. I may just go back to red sea alk additive even though I haven't had this problem before with the soda ash.

 

[Copingwithpods]

So I put in 120ml and I raised the alk by 0.6 (75 tank and sump is somewhere around 20 gal). Brs calculator is way lower then that which confuses me. I put another 60+ml in and it didn't go up at all from that. I may just go back to red sea alk additive even though I haven't had this problem before with the soda ash.

How quickly are you adding it to the tank? Is your sand clumped up and crunchy? Adding it too quickly like just pouring it in will definitely precipitate it out even if added to a high flow area

 

[phillygeeks]

That's why I asked: you really are not dosing huge amounts. 60 mL means less than 1 dKH per day. Even some soft coral tanks can use 2 dKH per day from coralline algae alone.

What is in the tank that might be using alk?

If you dose and do not measure until the evening, the tank may just be using it.

I might switch to baking soda for a while to let the pH drop back and reduce the potential for precipitation, but the consumption may be normal.

I had a similar issue and essentially what I didn't realize is that my sand turned to a solid piece of stone and that is where the alk was being consumed. I think when I switched to baking soda as Randy suggests here the issue sorted itself out. I think I probably have a similar post with a similar suggestion from Randy in my history somewhere.

 

[Randy Holmes-Farley]

So I put in 120ml and I raised the alk by 0.6 (75 tank and sump is somewhere around 20 gal). Brs calculator is way lower then that which confuses me. I put another 60+ml in and it didn't go up at all from that. I may just go back to red sea alk additive even though I haven't had this problem before with the soda ash.

There are different alkalinity supplements of different potency. Those made from sodium carbonate are twice as potent as those made from sodium bicarbonate. So if you get an answer very different from a calculator and are sure you made the recipe correctly (which also varies), be sure to check that you have the right entry in calculators.

 

[Randy Holmes-Farley]

So I put in 120ml and I raised the alk by 0.6 (75 tank and sump is somewhere around 20 gal). Brs calculator is way lower then that which confuses me. I put another 60+ml in and it didn't go up at all from that. I may just go back to red sea alk additive even though I haven't had this problem before with the soda ash.

Switch to baking soda if precipitation is a concern.

 

[Spare time]

Switch to baking soda if precipitation is a concern.

One more question for you. Why doesn't sodium bicarbonate lead to a lower pH over time? I was thinking that since bicarbonate is going to be bringing hydrogen into the tank vs sodium carbonate, how does this not decrease the ph in the long run? (ps forgive me if this is a dumb question, I am by no means a chemist).

 

[Randy Holmes-Farley]

One more question for you. Why doesn't sodium bicarbonate lead to a lower pH over time? I was thinking that since bicarbonate is going to be bringing hydrogen into the tank vs sodium carbonate, how does this not decrease the ph in the long run? (ps forgive me if this is a dumb question, I am by no means a chemist).

It leads to a tiny pH lowering by adding some CO2, where carbonate leads to a big pH boost by consuming CO2, and limewater/kalkwasser leads to a bigger ph boost by consuming about twice as much CO2, all per unit of alk added.

But all of these effects only last until the tank re-equilibrates that CO2 change with the air around the tank.
I show that experimentally here:

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH

Randy answers many questions in this complex relationship.

reefs.com

from it:

Alkalinity Supplements
One of the most common issues that reefkeepers face involves supplementing alkalinity while maintaining a reasonable pH. Alkalinity supplements impact pH in a variety of ways. One of these ways is the immediate altering of the pH. Different alkalinity supplements have different immediate impacts on pH, as most reefkeepers are aware. This impact is why, for example, limewater needs to be added slowly to a tank but sodium bicarbonate does not.

For this discussion, let’s presume that we want to supplement the carbonate alkalinity of a reef tank. That is, in the end we want to increase the bicarbonate and carbonate levels in the tank. There are a variety of ways to achieve this end, and these different ways have different immediate impacts on pH. Three of these ways (and combinations thereof) are fairly common in reefkeeping. These ways are addition of bicarbonate, carbonate, and hydroxide. In a reef tank that is permitted to equilibrate its total CO2 levels with the atmosphere, these additions all end up with the same final pH. That is, it is only the amount of alkalinity added that determines the final pH, not the nature of the additive itself.

In the short term, however, the impact on pH is very different. To quantify this, I measured to pH change on adding 0.5 meq/L of each of these alkalinity supplements to freshly made salt water (Instant Ocean made to S=35; alkalinity measured to be 2.26 meq/L by titration). Here’s the result for the pH found immediately, and then after 24 and 120 hours of sitting, unstirred, in an open 500- mL beaker:

Supplement	Initial pH	24 hour pH	120 hour pH
none	8.10	8.11	8.21
0.5 meq/L HCO3-	8.06	8.15	8.33
0.5 meq/L CO3–	8.44	8.28	8.34
0.5 meq/L OH-	8.76	8.47	8.33
0.5 meq/L H+	6.91	7.91	8.15

From this data it is clear to see the large increase in pH caused by the addition of hydroxide, and also the significant increase when using carbonate. Bicarbonate, on the other hand, shows the expected slight decrease in pH, but not nearly as much as is found with a strong acid of equal concentration. It is also clear that after sufficient time to equilibrate with atmospheric CO2, these differences disappear, and the pH is the same for all of the 0.5-meq/L alkalinity additions. This is an important result: in seawater in equilibrium with the atmosphere, for a given alkalinity there is a single pH that results, regardless of what was added to get to that alkalinity.

Here’s how to think of these additions. When these chemicals are added to the water, there is a change in the relative concentrations of carbonate and bicarbonate, and it is the ratio of these two ions that determines the pH.

 

[bdare]

For adjustments I've always found that baking soda works best. This helps keep the possibility of precipitation down.

 

[Spare time]

Thank you all very much