Why does dosing Nitrates drive down Alkalinity?

[Dom]

I've been dosing nitrates to a new tank (204 days old), which had undetectable nitrates.

Dosing over the last 6 weeks, I've been able to get nitrates up to 4ppm.

But why does my Alkalinity go down?

I've been dosing 8 grams of baking soda (cooked for a pH boost). But I've noticed the Alkalinity has gone down a full point (from 8.5 to 7.5). I've increased my daily dosing of bicarbonate to 9 grams starting yesterday.

I accept as fact that dosing nitrates drive down Alkalinity, but I would like to understand why adding nitrates causes this to happen.

Thank you,
Dom

 

[mjw011689]

Maybe one of the chemists here can chime in, but I don’t think it actually drives down nitrate, at least not directly. I dose nitrates on several different tanks but they all maintain a normal alk drop per day. I might drop .1 alk over a day or 2. I wouldn’t consider that to be a lot.

Do you have a lot of corals? What you might be seeing is growth driving alk down. I could see where once nitrates are in a range that certain corals like, they begin to grow more, which in turn causes them to use up alk faster. I have no testing to back this, I just haven’t ever heard that nitrate dosing causes drops in alk. And I definitely haven’t experienced it despite dosing nitrate on 4+ tanks

 

[Dom]

Maybe one of the chemists here can chime in, but I don’t think it actually drives down nitrate, at least not directly. I dose nitrates on several different tanks but they all maintain a normal alk drop per day. I might drop .1 alk over a day or 2. I wouldn’t consider that to be a lot.

Do you have a lot of corals? What you might be seeing is growth driving alk down. I could see where once nitrates are in a range that certain corals like, they begin to grow more, which in turn causes them to use up alk faster. I have no testing to back this, I just haven’t ever heard that nitrate dosing causes drops in alk. And I definitely haven’t experienced it despite dosing nitrate on 4+ tanks

Well, the idea behind dosing is to compensate for consumption of elements by the tank.

My Alkalinity was dialed in at 8.5 dosing 8 grams of bicarbonate daily. I've had to increase bicarbonate by 1 gram daily to push it back up, so I don't think consumption by the tank is the complete cause, although, it does play a role.

 

[Seansea]

Your corraline growing like crazy? Corrilane like nitrate as its an algae and it will rip alk down pretty good.

 

[Dom]

Your corraline growing like crazy? Corrilane like nitrate as its an algae and it will rip alk down pretty good.

Funny you should mention this; of my tanks, this is the only one that doesn't have Coralline growth.

 

[Seansea]

hmm interesting. I dose nitrates but my alk is pretty steady on its daily uptake. I dose 5ml of neonitrate per day and lose about .4 alk per day which i dose with afr. Havent noticed any correlation between nitrate uptake and alk compsumption to this point.

 

[Dom]

hmm interesting. I dose nitrates but my alk is pretty steady on its daily uptake. I dose 5ml of neonitrate per day and lose about .4 alk per day which i dose with afr. Havent noticed any correlation between nitrate uptake and alk compsumption to this point.

Yes, I think @Randy Holmes-Farley recently discussed this. I have to do a search.

 

[Reefer Matt Verified Media Partner]

I am curious as to why people dose nitrate, as opposed to adding more fish, feeding more, or turning off the skimmer and refugium (if equipped). I am actually curious, and not judgmental at all. The opposite problem of too high of nutrients used to be common, but somehow what was easy to achieve then, is difficult for many now. Thanks!

 

[mjw011689]

Because I’m running a heavily stocked tank with no fuge or skimmer and regularly drop down to zero on nitrates. I simply can not get nitrates to rise. I’m not going to drastically over feed because for one, the leftovers can turn into worse crud than just dealing with nitrate, and 2, I can’t measure how many nitrates I will gain from a cube of food. With dosing, I know exactly what my number will be based on the math, and 9 outta 10 it lands right where I expected.

 

[Reefer Matt Verified Media Partner]

Because I’m running a heavily stocked tank with no fuge or skimmer and regularly drop down to zero on nitrates. I simply can not get nitrates to rise. I’m not going to drastically over feed because for one, the leftovers can turn into worse crud than just dealing with nitrate, and 2, I can’t measure how many nitrates I will gain from a cube of food. With dosing, I know exactly what my number will be based on the math, and 9 outta 10 it lands right where I expected.

Thank you. I wonder what is removing the nitrate so fast? Is there a lot of coral taking up the nutrients?

 

[Seansea]

Ya what mjw said. Easier control of it. But i notice a huge difference in the way my zoa and cloves look when there is some nitrate and none. My algae scrubber strips alot of nutrients down so need to put them back in.

 

[mjw011689]

Thank you. I wonder what is removing the nitrate so fast? Is there a lot of coral taking up the nutrients?

Yeah, specifically coral that like some nutrients as well. I find euphyllia really does a number on my nitrates and phosphate

 

[Reefer Matt Verified Media Partner]

Yeah, specifically coral that like some nutrients as well. I find euphyllia really does a number on my nitrates and phosphate

Makes sense. Thanks!

 

[Dan_P]

I am curious as to why people dose nitrate, as opposed to adding more fish, feeding more, or turning off the skimmer and refugium (if equipped). I am actually curious, and not judgmental at all. The opposite problem of too high of nutrients used to be common, but somehow what was easy to achieve then, is difficult for many now. Thanks!

If the goal is a nitrate concentration in the water, just add it. The round about way of overfeeding fish to create more ammonia so it can be converted to nitrate is unnecessarily complex. Overfeeding fish can also contribute to higher dissolved organic carbon in the water.

 

[Randy Holmes-Farley Verified Community Expert]

FWIW, if you dose nitrate and that nitrate is consumed, that actually adds alkalinity. Each 50 ppm nitrate consumed adds 2.3 dKH.

If you are seeing a different effect, then that may be due to calcifying organisms growing faster with more N available.

 

[mjw011689]

FWIW, if you dose nitrate and that nitrate is consumed, that actually adds alkalinity. Each 50 ppm nitrate consumed adds 2.3 dKH.

If you are seeing a different effect, then that may be due to calcifying organisms growing faster with more N available.

Is this only true if you dose nitrate, or does it also apply to just having high nitrates that are being consumed by coral? Reason I ask, I’ve got a buddy who’s got fairly high nitrates, but his alk is constantly pushing 14, despite his salt mixing to 11. He doesn’t dose nitrate though, I think just high from a heavy bio load and feeding

 

[Miami Reef]

Is this only true if you dose nitrate, or does it also apply to just having high nitrates that are being consumed by coral?

Dosing nitrates bypasses the initial alk lowering reaction.

Food/ammonia added that turns into nitrates = loss of alkalinity

Nitrates that is consumed = same alk added back

It’s a net 0. No gain nor loss.

If you dose nitrates, the alkalinity will rise 2.3dKH for every 50ppm nitrates dosed and consumed.

 

[Miami Reef]

Reason I ask, I’ve got a buddy who’s got fairly high nitrates, but his alk is constantly pushing 14, despite his salt mixing to 11. He doesn’t dose nitrate though, I think just high from a heavy bio load and feeding

Accumulating nitrates from ammonia/food that isn’t getting consumed will lower the alkalinity.

If the nitrates is getting consumed, then it will be a net 0.

There must be another reason why his alk is rising.

 

[Randy Holmes-Farley Verified Community Expert]

Agree. Unless nitrate is actually declining or being dosed and consumed, there's no net impact on alk.

In a very low calcification system, slow dissolution of rock and sand can add alk, but 14 dKH seems unusual.

You sure he is not using tap water or adding anything that might boost alk without him knowing it? Tap water? pH boosters?

 

[mjw011689]

Agree. Unless nitrate is actually declining or being dosed and consumed, there's no net impact on alk.

In a very low calcification system, slow dissolution of rock and sand can add alk, but 14 dKH seems unusual.

You sure he is not using tap water or adding anything that might boost alk without him knowing it? Tap water? pH boosters?

Positive. I’ve seen his setup, and I also confirmed his rodi is still reading zero on a tds meter, so I have to assume that’s good. I’ve also tested it with my Hanna alk checker, which is also what he used. We’ve used multiple reagents and each time we’re within .1 of all the other readings. Nothing is being dosed in the tank, just water changes using Red Sea coral pro. I know Red Sea is on the high side, but not THAT high. I also checked salinity to make sure it wasn’t way over mixed.

Sorry for hijacking this thread!