Understanding Relationship between Alkalinity, Calcium, and Nitrates

[Nasty_Goblin]

Hello All,

I'm still rather new to reefing and I'm hoping for some help breaking down some changes in my aquarium of late.

I have a 10 gallon mixed reef. Mostly softies with a couple of LPS, monti's, and leptos.

As of March 8th, my parameters were:

Alk: 8.7 dKH
Calcium: 380 ppm (salifert)
Nitrates: 13.2 ppm
Phosphates: .01ppm
Magnesium: 1500 ppm
Salinity: 1.025

On the 10th I dosed 5ml of Calcium, 3ml Calcium on the 12th, and continued this trend of 3ml until I could maintain a Calcium level of 400 ppm.

During this time my Alkalinity rose to 9.6 dKH.

Nitrates remained in the 10-15 ppm range.

By the 23rd I was only dosing 1.8 ml of Calcium to keep this number consistent. The 24th was the last day that I dosed anything outside feeding.
I feed AB+ (4ml) 2-3 times a week and a mix of TDO and Benepets on the days I don't feed AB+. My clownfish gets a couple pellets 1-2 times a day.


By the 26th my parameters were:

Alk: 9.9 dKH
Calcium: 410 ppm (salifert)
Nitrates: 7.9 ppm
Phosphates: .03
Magnesium: 1500 ppm
Salinity: 1.026

On the 28th parameters were:

Alk: 10 dKH
Calcium: 440 ppm (API)
Nitrates: 7.9 ppm
Phosphates: .03
Magnesium: 1500 ppm
Salinity: 1.026

On this day I replaced benepets with reef-roids (I belive this was a mistake now).

March 29th my parameters were:

Alk: 10.6 dKH
Calcium: 480 ppm (salifert)
Nitrates: 17.6 ppm
Phosphates: .40
Magnesium: 1500 ppm
Salinity: 1.026


I performed a 30 percent water change, dropping my Alk and Calcium to 9.5dKH and 460ppm respectively.

March 30th my Alk was 10.4 dKH while my nitrates were 5.2.

I performed a 10 percent water change. Post water change Alk was 9.9 dKH and Nitrates were 2.3 ppm

Today my Alk was back to 10.5 dKH while my Nitrates rose to 3.4

My mixed saltwater tests 9.3 dKH while my RODI water tests 2.5 dKH.

I run filter floss and a protein skimmer for filtration. I have not dosed anything since the 24th. Is this cause for concern? I'd like to get ahead of this if I can, but I worry about such frequent water changes. What am I missing? It's clear to me that I lack a basic understanding of chemistry, I do not understand what is consistently raising Alkalinity.

 

[Randy Holmes-Farley]

I’m not sure what exactly the question is, but a few thoughts…

1. Don’t try to interpret small alk or calcium changes as they may just be test error.

2. Ro/di water at 0 ppm tds has zero alk. The 2.5 dKH is test error, or the water is not well purified.

3. All of the alk and calcium values you have posted are fine. No need to fixate on a single value as perfect.

4. Instead of dosing calcium, raising the salinity to ocean average 35 ppt (sg = 1.0264) will raise calcium to natural levels.

5. In a very low demand tank, alk may rise from slow dissolution of rock and sand. If that is the case, you may want to use or make a lower alk salt mix for water changes,

 

[MikeyZo]

The way I understand it, calcium and alkalinity have an inverse relationship, so as one goes up, the other comes down. Now magnesium is the buffer between the two. It helps keep calcium in suspension so it can be readily available for corals and such. If it’s too low, calcium will precipitate out as calcium carbonate (snow). If magnesium is too high (which yours is a bit) I think it throws off the relationship between alkalinity and calcium.

I also believe salinity plays a role in alkalinity, if you’re salinity is too high, alkalinity will rise.

 

[Nasty_Goblin]

I’m not sure what exactly the question is, but a few thoughts…

1. Don’t try to interpret small alk or calcium changes as they may just be test error.

2. Ro/di water at 0 ppm tds has zero alk. The 2.5 dKH is test error, or the water is not well purified.

3. All of the alk and calcium values you have posted are fine. No need to fixate on a single value as perfect.

4. Instead of dosing calcium, raising the salinity to ocean average 35 ppt (sg = 1.0264) will raise calcium to natural levels.

5. In a very low demand tank, alk may rise from slow dissolution of rock and sand. If that is the case, you may want to use or make a lower alk salt mix for water changes,

Thanks for the reply! I guess I have a few questions.

Are my numbers safe? What do I do if my Alk continues to rise? I'm worried about what will happen if I stop doing water changes.

 

[Nasty_Goblin]

The way I understand it, calcium and alkalinity have an inverse relationship, so as one goes up, the other comes down. Now magnesium is the buffer between the two. It helps keep calcium in suspension so it can be readily available for corals and such. If it’s too low, calcium will precipitate out as calcium carbonate (snow). If magnesium is too high (which yours is a bit) I think it throws off the relationship between alkalinity and calcium.

I also believe salinity plays a role in alkalinity, if you’re salinity is too high, alkalinity will rise.

My salinity is stable at 1.025-1.026 I was under the impression that this kind of fluctuation was normal and not cause for my Alk to rise so consistently.

I dont see any precipitation in my tank, water is clear. My magnesium is generally on the higher side. Always between 1300-1500.

I read that falling nitrates can raise alkalinity. So I assume raising nitrates would lower alkalinity?

 

[MikeyZo]

I think that once magnesium goes to high it starts to raise alkalinity

I’ve never heard of nitrate specifically affecting alkalinity. I’m not saying it doesn’t, I’ve just never heard of it. And I would assume that you would need one heck of a swing in nitrates to make that happen.

 

[MikeyZo]

If I was a betting man, I would say that it’s because you magnesium is too high. Try to get it down to the 1350-1425 range

 

[Randy Holmes-Farley]

Thanks for the reply! I guess I have a few questions.

Are my numbers safe? What do I do if my Alk continues to rise? I'm worried about what will happen if I stop doing water changes.

Yes, I said they were all fine. I also expect the magnesium is test error and I advise not testing it. Unless you have dosed it, it’s exactly the level in the salt mix no matter what a kit says.

 

[Nasty_Goblin]

I think that once magnesium goes to high it starts to raise alkalinity

I’ve never heard of nitrate specifically affecting alkalinity. I’m not saying it doesn’t, I’ve just never heard of it. And I would assume that you would need one heck of a swing in nitrates to make that happen.

What would be the best way to go about lowering my magnesium levels?

 

[Randy Holmes-Farley]

I think that once magnesium goes to high it starts to raise alkalinity

I’ve never heard of nitrate specifically affecting alkalinity. I’m not saying it doesn’t, I’ve just never heard of it. And I would assume that you would need one heck of a swing in nitrates to make that happen.

No, that’s just not true.

Magnesium never raises alkalinity and falling nitrate does.

 

[Randy Holmes-Farley]

What would be the best way to go about lowering my magnesium levels?

Do not do anything about magnesium.

 

[MikeyZo]

Best way I know of is just to do water changes, and if you’re using your own salt mix try to find one maybe that has a lower magnesium level in it

 

[Randy Holmes-Farley]

Best way I know of is just to do water changes, and if you’re using your own salt mix try to find one maybe that has a lower magnesium level in it

Let’s not confuse the op with advice about magnesium.

 

[MikeyZo]

Right not directly but if your magnesium is too high, then you’re holding too much calcium carbonate, which will raise your alkalinity. Otherwise no one would care about magnesium being too high

 

[Nasty_Goblin]

Yes, I said they were all fine. I also expect the magnesium is test error and I advise not testing it. Unless you have dosed it, it’s exactly the level in the salt mix no matter what a kit says.

Understood, so it seems like there is no cause for concern? I suppose I want to know how high my Alk can get before I should start to worry?

I will leave magnesium alone. I do get my RO water from the lfs I suppose its possible their filters need to be changed.

 

[Randy Holmes-Farley]

Right not directly but if your magnesium is too high, then you’re holding too much calcium carbonate, which will raise your alkalinity. Otherwise no one would care about magnesium being too high

I have almost never done this, but I am asking you to please stop giving advice in this thread as much of it is incorrect and is just confusing the op.

 

[MikeyZo]

My intent wasn’t to confuse. I was going by what I thought was correct. If I was wrong, I apologize and stand corrected.

 

[Randy Holmes-Farley]

Understood, so it seems like there is no cause for concern? I suppose I want to know how high my Alk can get before I should start to worry?

I will leave magnesium alone. I do get my RO water from the lfs I suppose its possible their filters need to be changed.

I recommend 7-11 dKH as a target range for alk and some salt mixes range up to 13 dKH, so it is not dangerous for your alk to rise a bit.

I recommend 400-550 ppm for calcium.

The alk may be rising if the ro water is really 2.5 dKH and looking for another source may be in order. I don’t suppose you have a tds meter to check it?

 

[Randy Holmes-Farley]

My intent wasn’t to confuse. I was going by what I thought was correct. If I was wrong, I apologize and stand corrected.

Not a problem.

The full relationships between these various things are described in these articles:

A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH by Randy Holmes-Farley - Reefkeeping.com

When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH ? Advanced Aquarist | Aquarist Magazine and Blog

 

[Nasty_Goblin]

I recommend 7-11 dKH as a target range for alk and some salt mixes range up to 13 dKH, so it is not dangerous for your alk to rise a bit.

I recommend 400-550 ppm for calcium.

The alk may be rising if the ro water is really 2.5 dKH and looking for another source may be in order. I don’t suppose you have a tds meter to check it?

I do not have a tds meter. Glad to hear I am overreacting, I will continue to hold off on dosing.

I will also recheck the alkalinity of my RO water and go to my original lfs for water. I had no issues using them before but they are a bit far away.