Alkalinity rising on its own - Need help please

[Freddie83]

Hello everyone!

After several weeks of research, my local reef club and I are absolutely stumped by what is causing the high alkalinity in my system.

Few specs:

-180g display tank
-40g sump with cheato
-Reef Octopus skimmer
- 2x250w metal halides with LEDs strip supplement
-130 lbd live rock
-180 pounds crushed coral

Parameters:
PH: 8.6
Calcium: 440
Alkalinity: 15 Dkh
Nitrate: 40ish (currently dosing NoPox)
Not entirely sure why Nitrate is so high as I don’t feed heavily.

I’ve been monitoring alkalinity for several weeks and it will bounce between 14.4 and 15.5, this issue began prior to me dosing NoPox.

My softies are doing well; however, the few stony corals I have have been starting to show their skeleton more and more each day.

I’ve never dosed two part nor any another additives other than NoPox, the salt I use for water changes has roughly 7 Dkh in alk.
The fresh water I use for top off has nearly 0 alk.

I used to keep my cheato lights on 24/7 but I’ve recently changed the timer to bring the sump lights on when the DT lights are off for the night.

Even with water changes the alkalinity will eventually creep back up. I’m not entirely sure what to do anymore.

Has anyone encountered a similar issue before?

Edit: I’ve tried adding some calcium to the tank to see if I could get Alk to drop to no avail.
The aquarium is well enclosed with a tight canopy on top which does not allow much fresh air to come in.

 

[Crabs McJones]

What test kit are you using? Only thing I could potentially see it coming from is the crushed coral

 

[laverda]

How are you dosing Calcium? Are you dosing anything else? Like purple up for example?

 

[Shanet]

I have this problem and the only thing I can put it down to is that I am using shell grit as sand. As the water heats up the alk increases, as it cools it decreases.

 

[Freddie83]

What test kit are you using? Only thing I could potentially see it coming from is the crushed coral

Salifert test kits.

Interesting idea about the crushed coral.

 

[Freddie83]

How are you dosing Calcium? Are you dosing anything else? Like purple up for example?

I used calcium as a one time thing from an EVS 2-part jug I had sitting around, and no, not diving anything else.

 

[shred5]

Do you do water changes and if you do check the saltwater you use for water changes.
Could be a bad bucket or bag of salt. I have had several bad batches of salt over the years.

 

[casper320]

I know exactly what this is because I experienced the same thing. Most people don't realize that alkalinity is consumed during the nitrogen cycle. At the end of the cycle, when nitrates turn to nitrogen gas, the alkalinity is released back into the water keeping it stable. This only happens when Nitrates are BELOW 50 ppm. What happened in your tank is you let your nitrates get past 50 and now that they are lowering below 50 and are releasing back into the tank. The carbonate was bound into your nitrates and are now released back into the tank.

source: https://www.researchgate.net/publication/241040412_Ammonia_in_Aquatic_Systems1
There was a advanced aquarist article where I got the number 50 from that I cant seem to find.

 

[Freddie83]

I know exactly what this is because I experienced the same thing. Most people don't realize that alkalinity is consumed during the nitrogen cycle. At the end of the cycle, when nitrates turn to nitrogen gas, the alkalinity is released back into the water keeping it stable. This only happens when Nitrates are BELOW 50 ppm. What happened in your tank is you let your nitrates get past 50 and now that they are lowering below 50 and are releasing back into the tank. The carbonate was bound into your nitrates and are now released back into the tank.

source: https://www.researchgate.net/publication/241040412_Ammonia_in_Aquatic_Systems1
There was a advanced aquarist article where I got the number 50 from that I cant seem to find.

I think you’re on to something here.
Did the issue solve itself once you were able to get nitrates down below an acceptable level?

 

[casper320]

I think you’re on to something here.
Did the issue solve itself once you were able to get nitrates down below an acceptable level?

Yes, this is what happened anecdotally for me in my 6 month old reef that had new sps frags in it;

My nitrates rose past 50+ due to my chaeto stopped growing (no iron). I was testing every day because I had new frags and wanted to dial in my alkalinity. I noticed my alkalinity dropped from 9.5 to 7dkh in a day. I thought my new frags just loved my tank at the time and were growing. This doesn't make sense in retrospect. I dosed my tank back to 9.5. I then dosed iron to drop my nitrates back down and as it went down to 20 my alkalinity rose up to 12dkh. I stopped dosing and I let my tanks alkalinity drop to its normal level. It dropped at a predictable rate after that.

 

[Freddie83]

Yes, this is what happened anecdotally for me in my 6 month old reef that had new sps frags in it;

My nitrates rose past 50+ due to my chaeto stopped growing (no iron). I was testing every day because I had new frags and wanted to dial in my alkalinity. I noticed my alkalinity dropped from 9.5 to 7dkh in a day. I thought my new frags just loved my tank at the time and were growing. This doesn't make sense in retrospect. I dosed my tank back to 9.5. I then dosed iron to drop my nitrates back down and as it went down to 20 my alkalinity rose up to 12dkh. I stopped dosing and I let my tanks alkalinity drop to its normal level. It dropped at a predictable rate after that.

This helps a lot. Are you suggesting to just keep working on bringing nitrates down and then alk will be consumed on its own?

 

[MnFish1]

This helps a lot. Are you suggesting to just keep working on bringing nitrates down and then alk will be consumed on its own?

According to multiple articles and posts from @Randy Holmes-Farley - its close to impossible for alkalinity in 'increase on its own'. If you leave it it will gradually decrease. SO - as to your question - are you checking Alkalinity at the same time each day? If not it will vary morning to night. Are you sure your test kits are actually 'accurate'? ie. double checked. I dont know about nitrate and alkalinity - (i.e. how much that would make a difference) - same with 'coral shells' at the pH of a marine aquarium (they should not release that much alkalinity unless the pH is quite low (or am I incorrect). Rather than the change between 14 and 15 - Im wondering how/why your alk is so high in the first place (ie. 14) - is there a dosing issue?

 

[casper320]

According to multiple articles and posts from @Randy Holmes-Farley - its close to impossible for alkalinity in 'increase on its own'. If you leave it it will gradually decrease. SO - as to your question - are you checking Alkalinity at the same time each day? If not it will vary morning to night. Are you sure your test kits are actually 'accurate'? ie. double checked. I dont know about nitrate and alkalinity - (i.e. how much that would make a difference) - same with 'coral shells' at the pH of a marine aquarium (they should not release that much alkalinity unless the pH is quite low (or am I incorrect). Rather than the change between 14 and 15 - Im wondering how/why your alk is so high in the first place (ie. 14) - is there a dosing issue?

It certainly is possible, I know for a fact my test kits were accurate because I used two different test kits and brought a sample into my lfs to double check both of my kits. Alkalinity is a function of the nitrogen cycle and that's a fact.

 

[casper320]

This helps a lot. Are you suggesting to just keep working on bringing nitrates down and then alk will be consumed on its own?

I think the best thing to do would be a large water change to get everything balanced out tbh.

 

[MnFish1]

It certainly is possible, I know for a fact my test kits were accurate because I used two different test kits and brought a sample into my lfs to double check both of my kits. Alkalinity is a function of the nitrogen cycle and that's a fact.

I have no doubt about your experience FWIW, I didn't say alkalinity was independent of the nitrogen cycle - just to be clear - what I was trying to say is that alkalinity does not increase 'on its own'. I also wasnt referring to your post - I was referring to the OP's post - which suggested that his alkalinity was bouncing up and down 7 percent or so - this is not the same as 'alkalinity constantly rising'. If I had to pick a reason for this I would rank the reasons: 1. varying timing of testing during the day. 2. testing error/natural variation in the tests (ie margin of error). 3. Another confounding issue timing of algae reactor, some compound confounding the test...

I looked at your article - searching for nitrate effects on alkalinity - I did not find it except the one diagram - and it didnt really show / quantify the change in alkalinity for a given change in nitrate. Most of the article related to ammonia - as compared to nitrate.

But - here would be my comment. The OP has a high alkalinity - despite not adding alkalinity - and using a salt mixture that mixes to 7. You propose that as nitrate drops alkalinity increases (I think that was your point - correct me if im wrong - and that in your tank your alkalinity dropped as your nitrates increased).

Say you start with a tank of freshly mixed saltwater DKH 7. And ignore any other possible affect on alkalinity (there are many) and you allow the nitrate to rise to lets say 50 with heavy feeding. During that time (based on your premise, the alkalinity should fall). If you then do something to decrease nitrate (feed your chaeto as you did) that alkalinity will rise. That said - it won't go from 7 to 15. It might go from 7 to 6 and then back to 7 during this little experiment.

BTW - Chaeto - and its growth/lack of growth can on its own affect alkalinity.

Not at all trying to disagree with you - but I cant fathom a way that salt mixed to an alkalinity of 7 - can get to 14 having anything to do with nitrate.

 

[casper320]

I have no doubt about your experience FWIW, I didn't say alkalinity was independent of the nitrogen cycle - just to be clear - what I was trying to say is that alkalinity does not increase 'on its own'. I also wasnt referring to your post - I was referring to the OP's post - which suggested that his alkalinity was bouncing up and down 7 percent or so - this is not the same as 'alkalinity constantly rising'. If I had to pick a reason for this I would rank the reasons: 1. varying timing of testing during the day. 2. testing error/natural variation in the tests (ie margin of error). 3. Another confounding issue timing of algae reactor, some compound confounding the test...

I looked at your article - searching for nitrate effects on alkalinity - I did not find it except the one diagram - and it didnt really show / quantify the change in alkalinity for a given change in nitrate. Most of the article related to ammonia - as compared to nitrate.

But - here would be my comment. The OP has a high alkalinity - despite not adding alkalinity - and using a salt mixture that mixes to 7. You propose that as nitrate drops alkalinity increases (I think that was your point - correct me if im wrong - and that in your tank your alkalinity dropped as your nitrates increased).

Say you start with a tank of freshly mixed saltwater DKH 7. And ignore any other possible affect on alkalinity (there are many) and you allow the nitrate to rise to lets say 50 with heavy feeding. During that time (based on your premise, the alkalinity should fall). If you then do something to decrease nitrate (feed your chaeto as you did) that alkalinity will rise. That said - it won't go from 7 to 15. It might go from 7 to 6 and then back to 7 during this little experiment.

BTW - Chaeto - and its growth/lack of growth can on its own affect alkalinity.

Not at all trying to disagree with you - but I cant fathom a way that salt mixed to an alkalinity of 7 - can get to 14 having anything to do with nitrate.

What I'm claiming is alkalinity is a function of the oxidation process of nitrogen. As the nitrogen oxidizes from ammonia through nitrate this is known as nitrification, this process consumes alkalinity as well as dissolved oxygen. The process of denitrification is when nitrates are converted to different forms of gasses and the final form is nitrogen gas. This process creates residual carbonate. This will raise alkalinity (the same that was consumed) thus balancing itself out.

In a balanced system we don't have to worry about the nitrogen cycles affect on alkalinity. However, he is dosing carbon to encourage anaerobic activity (denitrification) which produces more alkalinity and because his nitrates are so high its causing his alkalinity to rise considerably.

Source: http://kisi.deu.edu.tr/orhan.gunduz/turkce/dersler/Nitrification_and_Denitrification.pdf

 

[casper320]

Nitrification consumes alkalinity
Denitrification replenishes alkalinity

My theory is:

If you create a condition where there is more denitrification occurring than nitrification i.e (nitrates >50ppm + carbon dosing). Your alkalinity will rise.

 

[MnFish1]

What I'm claiming is alkalinity is a function of the oxidation process of nitrogen. As the nitrogen oxidizes from ammonia through nitrate this is known as nitrification, this process consumes alkalinity as well as dissolved oxygen. The process of denitrification is when nitrates are converted to different forms of gasses and the final form is nitrogen gas. This process creates residual carbonate. This will raise alkalinity (the same that was consumed) thus balancing itself out.

In a balanced system we don't have to worry about the nitrogen cycles affect on alkalinity. However, he is dosing carbon to encourage anaerobic activity (denitrification) which produces more alkalinity and because his nitrates are so high its causing his alkalinity to rise considerably.

Source: http://kisi.deu.edu.tr/orhan.gunduz/turkce/dersler/Nitrification_and_Denitrification.pdf

Thanks - this is the key sentence from the article:
Denitrification is an alkalinity producing process. Approximately 3.0 to 3.6 pounds of alkalinity (as CaCO3) is produced per pound of nitrate, thus partially mitigating the lowering of pH caused by nitrification in the mixed liquor.

Suggesting that the first parts of the nitrogen cycle consume alkalinity - the conversion of nitrate to N2, etc increase alkalinity - but it only Partially mitigates the lowering of PH - it doesnt exceed it.

In other words for the nitrate to have gotten to 50 in the first place - the alkalinity must have dropped. When the Nitrate goes down (to zero lets say) - it will rise (this will happen simultaneously in a balanced tank - right)?

unless he is actively adding nitrate to his tank (which he says he is not) there is no way that just lowering nitrate will cause saltwater mixed at 7 to rise to 14/15. I completely agree with you that short-term fluctuations in the use of chaeto, addition/removal of coral, etc that could affect nitrate - may cause alkalinity to fluctuate. I think the OP has a different problem. (IMHO). But its an interesting discussion

 

[MnFish1]

What I'm claiming is alkalinity is a function of the oxidation process of nitrogen. As the nitrogen oxidizes from ammonia through nitrate this is known as nitrification, this process consumes alkalinity as well as dissolved oxygen. The process of denitrification is when nitrates are converted to different forms of gasses and the final form is nitrogen gas. This process creates residual carbonate. This will raise alkalinity (the same that was consumed) thus balancing itself out.

In a balanced system we don't have to worry about the nitrogen cycles affect on alkalinity. However, he is dosing carbon to encourage anaerobic activity (denitrification) which produces more alkalinity and because his nitrates are so high its causing his alkalinity to rise considerably.

1. If a constant amount of carbon is being added daily - it is a balanced system. If he is adding carbon one day and skipping 3 days - what you're suggesting is true. (just like if one adds the same amount of fish food daily - its a balanced system).
2. All 'added carbon' does not enter the denitrification cycle. Its also used by non anaerobic bacteria etc.

If point #1 were not the case - we would not need to add alkalinity (in the form of 2 part) to our tanks - as it would constantly be increasing due the the various forms of carbon we're adding to our tanks. Certainly - if this process is capable of changing the alkalinity of a saltwater solution from 7 to 14..... Of course corals use alkalinity. Every time an acid is released into the water (of any kind) it lowers alkalinity, corals used carbonate, etc. My only point is not to argue basic chemistry with which I agree on your points - but merely to state that it cant explain whats happening in this guy's tank

 

[casper320]

I think you're missing my point. I'm not sure how the condition was met, I'm just saying that it currently is in that condition and that if the condition is met it is possible to have the alkalinity raise on its own.

What I imagine happened was in the earliest stage of the nitrate problem happening his alkalinity probably lowered and he corrected it by adding 2 part. Eventually when his nitrates were lowered rapidly it added the additional alkalinity that he can't account for. In my case I dosed 2 part to compensate for a sudden drop in 2dKh and that 2dKh would eventually have been replenished, thus resulting in an increase from 9.5 to around 12dkH.