Relationship between nitrate and alk

[recess62]

Will someone please explain the relationship between nitrate levels and Alk. My Nitrate run 10-25. When I reload by biopellets the nitrates drop and I get an Alk spike which invariably my corals do not like.

 

[Randy Holmes-Farley]

There is no "direct" relationship.

The conversion of ammonia to nitrate depletes alkalinity, so if nitrate is rising, then alkalinity can be depleted by this process.

The consumption of nitrate by any process (except a water change) gives back the exact amount of alkalinity when it was made. So if nitrate is declining, that process will add to alkalinity.

So if nitrate is steady, and is coming from ammonia, then it should not impact the alkalinity.

If you are dosing nitrate that is being consumed, that is effectively boosting alkalinity a small amount.

 

[recess62]

So when I add pellets and the population of bacteria within the reactor increases and thus comsumes the nitrates this gives back the alk that was consumed when the ammonia was nitrified. Is there any way to predict the amount of alk rise. So that I can dial back on my dosing pump?

 

[Randy Holmes-Farley]

So when I add pellets and the population of bacteria within the reactor increases and thus comsumes the nitrates this gives back the alk that was consumed when the ammonia was nitrified. Is there any way to predict the amount of alk rise. So that I can dial back on my dosing pump?

Yes:

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.

The exact same value will be true in reverse (e.g., 50 ppm nitrate consumed by bacteria on biopellets).

I discuss such issues here:
When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2004-12/rhf/index.htm

 

[recess62]

Once again TY Dr Farley

 

[Randy Holmes-Farley]

You're welcome.

Happy Reefing.

 

[Skynyrd Fish]

Good info.

 

[LRT]

There is no "direct" relationship.

The conversion of ammonia to nitrate depletes alkalinity, so if nitrate is rising, then alkalinity can be depleted by this process.

The consumption of nitrate by any process (except a water change) gives back the exact amount of alkalinity when it was made. So if nitrate is declining, that process will add to alkalinity.

So if nitrate is steady, and is coming from ammonia, then it should not impact the alkalinity.

If you are dosing nitrate that is being consumed, that is effectively boosting alkalinity a small amount.

Still trying to get my head wrapped around this here.
As you know I've been running high alkalinity around 12.2 currently.
My nitrates are super low almost 0 on API test.
If I dose amino acids and bring my nitrates up will this bring my alkalinity down?
I'm just not getting how this all works together I guess!

On edit*
I ordered a new rodi. When I mix salt with my current ro system I'm getting a 14+ alkalinity at 1.025 with 2 different salt mixes.
Calcium and magnesium in correct ranges for salt mix designs just ending up with high Alk.
Could it be that my current ro system is just coming out high alk and the salt mix is adding to the alkalinity?
Not really sure how to test my ro water alkalinity without salt being mixed to it.
Really struggling with this!

 

[Randy Holmes-Farley]

Dosing amino acids to boost nitrate to 5 ppm will deplete 0.2 dKH of alkalinity. If then nitrate stays at 5 ppm or lower by more dosing, there will be no additional ongoing depletion of alk.

 

[Randy Holmes-Farley]

You can test your source water with a normal alk kit. If it is 0-1 ppm tds, the alk is low.

 

[LRT]

Ok think I'm going to dose amino to get my nitrates up to 5 either way.
My current coralife 3 stage ro is producing 118 ppm. Could this be causing the high alkalinity?
I have a 6 stage rodi on the way I'm just going to have to wait and gradually bring all back down.
When you say regular alk test to test rodi water can you reccomend one?
I'm currently using the hanna meter with reagents not sure if I can test regular ro water with out mixing salt to it..?

 

[Randy Holmes-Farley]

118 ppm tds? Yes, could have a ton of alk.

it might even be higher than the incoming water.

 

[Randy Holmes-Farley]

any normal alk test, such as Salifert, that you are using for the aquarium can be used in Ro/di. I’m not 100% sure on the Hanna, but I’d try it and think it is ok.

 

[LRT]

any normal alk test, such as Salifert, that you are using for the aquarium can be used in Ro/di. I’m not 100% sure on the Hanna, but I’d try it and think it is ok.

Awesome sir thank you for all your help on this topic!

 

[Salty_Northerner]

Great info!