What caused my alk spike?

[PranK]

Hi All,

My tank has been quite stable for a while. Roughly a 225G system (~900L).
I dose 2+1 part (Randy's formula) and also Nopox. All via Jebao doser (cheapie, I know, but regular checks have been spot on).
Until recently I was also running GFO (Phosban).

Numbers;
pH ~8.4
Salinity 1.027
Calcium 420
Mag 1400
Phos ~0.2
Nitrates 5ppm
Alk was between 8.5 and 9.0 day in and day out for years.

Now, on the 15th of November, I tested alk at 9. Then on the 25th of Nov I tested it at 11.7.

The only two changes between those dates was removing the GFO and also I took a basket of rock rubble out (not much ~15kg which I think is ~6lbs). I also redirected my sump flow to go through my bio bricks (this brought nitrate down from ~20 to 5ppm).

At the same time as this alk spike, I ran out of the Hanna reagent for alk, so I ordered some fresh stuff and it confirmed the values a few days after.

I have dropped the alk dosing down, bit by bit, we've taken the total 24 dose from 140mls to 88mls. Which, seems like a lot! Last test 2 days ago has alk at 10.7.

A lot of my SPS are showing algae on tips, proving (?) alk burn.

I'm trying to get it back down to 9-ish. I'm not a number chaser as such, I just want stability and things looked good at 9.

I guess I'm wondering what I changed that caused this spike ?

I know it seems like a no brainer - the GFO caused it. But I have read conflicting info about whether GFO will cause alk changes and I was hoping to confirm or deny that theory in here.

Thanks in advance.

Christian

 

[Randy Holmes-Farley]

It may partly be test error. You only "confirmed" the second reading, not the first one.

The nitrate declined added some alk, the GFO removal may have reduced some calcium carbonate precipitation.

While it is not an effect of the GFO itself, There is no significant debate that iron can initiate precipitation of calcium carbonate. Many folks see it on the GFO, or downstream of it.

 

[92Miata]

The big nitrate drop/etc may have also slowed coral uptake - which would cause your stable dosing to be too high.


I've had issues with my Hanna meter reading really low towards the end of bottles also.

 

[PranK]

It may partly be test error. You only "confirmed" the second reading, not the first one.

The nitrate declined added some alk, the GFO removal may have reduced some calcium carbonate precipitation.

While it is not an effect of the GFO itself, There is no significant debate that iron can initiate precipitation of calcium carbonate. Many folks see it on the GFO, or downstream of it.

Thanks so much for the reply Randy.
Can you elaborate on this "The nitrate declined added some alk" - do you suggest similar to 92Miata below, that coral uptake declined due to lower nitrates?
Ok, so perhaps my first test was low? Alk may have been climbing for some time.

The big nitrate drop/etc may have also slowed coral uptake - which would cause your stable dosing to be too high.


I've had issues with my Hanna meter reading really low towards the end of bottles also.

Thanks for the reply
Might be worth getting a second kit ... I just feel like its a bit wasteful.
Good theory with the nitrate drop, that makes sense to me.

 

[Randy Holmes-Farley]

Thanks so much for the reply Randy.
Can you elaborate on this "The nitrate declined added some alk" - do you suggest similar to 92Miata below, that coral uptake declined due to lower nitrates?
Ok, so perhaps my first test was low? Alk may have been climbing for some time.



Thanks for the reply
Might be worth getting a second kit ... I just feel like its a bit wasteful.
Good theory with the nitrate drop, that makes sense to me.

While that may be true, what I am saying is that the consumption of nitrate itself releases alkalinity, and the production of nitrate depletes alkalinity.

Thus, when nitrate is rising, alk is being depleted. When nitrate is falling (except by water change), alk is ruising.

The exact amount is about 4.5 dKH for each 50 ppm of nitrate produced or consumed.

I discuss it here:

http://reefkeeping.com/issues/2004-12/rhf/index.htm

from it:

Alkalinity Decline in the Nitrogen Cycle

One of the best known chemical cycles in aquaria is the nitrogen cycle. In it, ammonia excreted by fish and other organisms is converted into nitrate. This conversion produces acid, H+ (or uses alkalinity depending on how one chooses to look at it), as shown in equation 1:

(1) NH3 + 2O2 --> NO3- + H+ + H2O
For each ammonia molecule converted into nitrate, one hydrogen ion (H+) is produced. If nitrate is allowed to accumulate to 50 ppm, the addition of this acid will deplete 0.8 meq/L (2.3 dKH) of alkalinity.

However, the news is not all bad. When this nitrate proceeds further along the nitrogen cycle, depleted alkalinity is returned in exactly the amount lost. For example, if the nitrate is allowed to be converted into N2 in a sand bed, one of the products is bicarbonate, as shown in equation 2 (below) for the breakdown of glucose and nitrate under typical anoxic conditions as might happen in a deep sand bed:

(2) 4NO3- + 5/6 C6H12O6 (glucose) + 4H2O --> 2 N2 + 7H2O + 4HCO3- + CO2

In equation 2 we see that exactly one bicarbonate ion is produced for each nitrate ion consumed. Consequently, the alkalinity gain is 0.8 meq/L (2.3 dKH) for every 50 ppm of nitrate consumed.

Likewise, equation 3 (below) shows the uptake of nitrate and CO2 into macroalgae to form typical organic molecules:

(3) 122 CO2 + 122 H2O + 16 NO3- --> C106H260O106N16 + 138 O2 + 16 HCO3-

Again, one bicarbonate ion is produced for each nitrate ion consumed.

It turns out that as long as the nitrate concentration is stable, regardless of its actual value, there is no ongoing net depletion of alkalinity. Of course, alkalinity was depleted to reach that value, but once it stabilizes, there is no continuing alkalinity depletion because the export processes described above are exactly balancing the depletion from nitrification (the conversion of ammonia to nitrate).

There are, however, circumstances where the alkalinity is lost in the conversion of ammonia to nitrate, and is never returned. The most likely scenario to be important in reef aquaria is when nitrate is removed through water changes. In that case, each water change takes out some nitrate, and if the system produces nitrate to get back to some stable level, the alkalinity again becomes depleted.

If, for example, nitrate averages 50 ppm at each water change, then over the course of a year with 10 water changes of 20% each, the alkalinity will be depleted by 1.6 meq/L (4.5 dKH) over the course of that entire time period. This process is one of the primary reasons that fish-only aquaria that often export nitrate in water changes need occasional buffer additions to replace that depleted alkalinity.

While the magnitude of the depletion described in the paragraph above is fairly easy to understand, it also can be converted into units that clarify the imbalance. The impact of alkalinity depletion on the calcium and alkalinity demand balance depends, of course, on the amount of calcium and alkalinity added (and consumed) over the course of that same year.

For a typical reef aquarium (assuming a daily addition of saturated limewater equal to 2% of the tank's volume), the amount of alkalinity added during the course of a year is 297.8 meq/L. Likewise, the amount of calcium added is 5,957 ppm Ca++, given the ratio of 1 meq/L of alkalinity for every 20 ppm of calcium that has been discussed above. If that 1.6 meq/L of alkalinity is added to create a larger demand of 299.4 meq/L over the course of a year, the new ratio for the total demand becomes 19.90 ppm Ca++ per 1 meq/L of alkalinity. Consequently, while this effect of nitrate production on alkalinity is enough to be noticed over the course of a year, it is substantially smaller than the other effects discussed in this article, and is unimportant for aquaria that maintain low nitrate levels.

 

[Fourstars]

So if you run a uln system and dose nitrate and phosphate will you still have a depletion of alkalinity? “alkalinity is lost in the conversion of ammonia to nitrate”

 

[Randy Holmes-Farley]

So if you run a uln system and dose nitrate and phosphate will you still have a depletion of alkalinity? “alkalinity is lost in the conversion of ammonia to nitrate”

No.

Dosing nitrate will add alkalinity.

There is no loss of alk from the ammonia to nitrate conversion in this context because the nitrate is being consumed, giving back exactly the alk that was lost in the ammonia to nitrate part of the process.

 

[PranK]

While that may be true, what I am saying is that the consumption of nitrate itself releases alkalinity, and the production of nitrate depletes alkalinity.

Thus, when nitrate is rising, alk is being depleted. When nitrate is falling (except by water change), alk is ruising.

The exact amount is about 4.5 dKH for each 50 ppm of nitrate produced or consumed.

This is amazing and explains it perfectly.

I went from roughly 25ppm nitrate and roughly 9dkh to 5ppm nitrate.

20ppm drop is 40% of 50ppm
40% of 4.5dkh is 1.8.

That 1.8 would have brought my alk up to high 10's or even 11.

I never knew that alk and nitrate were affected in this way. Even more evidence that stability of all your elements is so important.

Thanks so much Randy, I really appreciate it.

 

[Randy Holmes-Farley]

You're welcome.

Happy Reefing.

 

[Hubtech]

OK so my tank nitrate is HIGH like 65+. phosphate is >200 PPM according to hanna (and has been for months). How would you recommend I get my nutrients back in check @Randy Holmes-Farley ?

Currently dosing 50ml/minute from my carx, and 1600ml/day through 12 doses from my kalk stirrer.

Water change? Carbon dose?

 

[Fourstars]

OK so my tank nitrate is HIGH like 65+. phosphate is >200 PPM according to hanna (and has been for months). How would you recommend I get my nutrients back in check @Randy Holmes-Farley ?

Currently dosing 50ml/minute from my carx, and 1600ml/day through 12 doses from my kalk stirrer.

Water change? Carbon dose?

You could also consider a refugium or algae turf scrubber.

 

[Randy Holmes-Farley]

OK so my tank nitrate is HIGH like 65+. phosphate is >200 PPM according to hanna (and has been for months).

That cannot be right unless you massively overdosed a phosphate additive. >200 ppm?

 

[Hubtech]

Phosphate is >200 according to the ultra low test. May be ppb. I have an ATS, skimmer.

 

[Brett S]

phosphate is >200 PPM according to hanna (and has been for months)

Is it possible that you’re using the Hanna Phosphorus ULR checker and not converting it? That reads phosphorus in ppb and the result needs to be multiplied by .003066 to convert to phosphate ppm. So a reading of 200ppb of phosphorus would actually be .61ppm of phosphate. Still quite high, but not crazy high like 200ppm.

 

[Hubtech]

It is the ultra low. Reading >200. Test result just blinks. Verified with two separate Hanna testers and reagent batches. Tanks happy.

 

[Randy Holmes-Farley]

It is the ultra low. Reading >200. Test result just blinks. Verified with two separate Hanna testers and reagent batches. Tanks happy.

OK, so your problem is a thousand times smaller than you first posted, and well within the range of phosphate in some fabulous reef tanks. lol

200 ppb phosphorus equals about 0.6 ppm phosphate.

To bring it down, I'd suggest more ongoing export, either by a refugium (which will also bring down nitrate), or by using a phosphate binder such as GFO or lanthanum. It will take a while because there is even more bound to rock and sand than this value.

Phosphate In The Reef Aquarium
https://www.reef2reef.com/blog/?p=3184

 

[Hubtech]

so i'll just continue with my ATS, and maybe carbon dose?

 

[PranK]

Hi @Randy Holmes-Farley - a quick question on your post above. I think I am reading that once the nitrate has stabilised again, the alkalinity *should* return to normal based on unchanged dosing ?

If this is the case I should monitor this a lot because I did change the dosing amount quite significantly.

Thanks again.

 

[Randy Holmes-Farley]

If you are not dosing nitrate, and nitrate is stable, then organic carbon dosing will not impact alkalinity unless it carries alkalinity itself, such as sodium acetate.

 

[PranK]

Thanks Randy. Alk is still a bit elevated (10.5) after dropping my dosing right down.

I'll stick with this for another week or so as my Nitrates are now down to 3 (never had them this low!!) so I'll see if any further changes and then adjust dose to bring be back to ~9.