Nitrates not being used up?!??

[hashbaz]

I just recently set up a high light 75g and my nitrates are not being used like I would expect.

Tank specs:
75gallon
220 Watts CF (3WPG) 12hr/day
Ecocomplete
Fully planted, including lots of fast growing stem-plants
15 fish (platies, guppies, cories)
Moved filter media over from previous tank
Dechlorinator: SeaChem Prime

I set up the tank just over a week ago and started with 15ppm of nitrate from Calcium Nitrate ( 5Ca(NO3)2.NH4NO3.10H2O ). In over week, my nitrates have only gone down to 10ppm.

Shouldn't my tank use a ton more nitrates? I have tons of plants, lots of growth and a small bio-load.

I'm guessing I am getting a false reading on my Aquarium Pharmaceuticals. Would Prime or Calcium Nitrate or something else give me a false reading on my test kit?

I've been meaning to take a water sample to a LFS to verify my results, but I worry that they have the same test kit.

I am also getting staghorn algae which can be caused by a shortage of macros.

I am considering adding 5ppm of KNO3 everyday just because I think it needs it - (along with 50% weekly water changes).

What do you folks think?

 

[Purrbox]

Most of the Nitrate kits available to us for a reasonable price aren't entirely reliable at measuring lower levels of Nitrate. I would recommend bumping your Nitrate to between 15-20ppm, as your kit should be able read the Nitrate at that level more accurately. It is possible that you are feeding your fish enough (overfeeding) to keep the Nitrates up, but I doubt it.

 

[czcz]

Agree. It could be that the plants have been capitilizing on NH4 from calcium nitrate and so have not significantly dropped NO3.

 

[fish_4_all]

With the tank being so new, could the plants be using the ammonia instead of the NO3?

 

[hashbaz]

All of this is assuming that my tank should be burning through nitrates. Should it?

I am guessing that the problem is not plants absorbing ammonia. There just is not enough ammonia. I have a small bio-load (and I don't think I'm over feeding - underfeeding is more likely) and the Calcium-Ammonium-Nitrate only added .25ppm ammonia over a week ago.

As purrbox suggested, I thought the testkit may be inaccurate. So I got out some RODI water, some KNO3, and a scale to test the accuracy of my test kit. The test kit measured 0ppm just fine, it also measured 5ppm just fine. But when I tested water with 10ppm, my test kit showed a little less than it should have. So if anything, my test kit is showing less NO3 than I actually have in there.

I'm wishing I knew more chemistry but my guess is that there is some Nitrate compound in my water that cannot be used by plants, but can still be measured with a nitrate test kit.

 

[czcz]

With your fast growth and low bioload/feeding, there *should* be a drop in nitrates greater than 5ppm/wk. There's the possibility the plants are limited by another nutrient, but growth should be limited, and presumably you're dosing the other macros and micros.

FWIW, your plan of adding some KNO3 and observing is good to me. I do not know if there are organic or inorganic compounds that would not register on the test, and it is over my head, but on Barr's site and APC there has been discussion that plants prefer inorganic NO3 (from KNO3, etc) to organic NO3 (from the biofilter), and some aquarists report pearling when adding KNO3 to tanks with available organic nitrogen. Might be worth poking around.

If it were my tank I would add the KNO3 and observe next week, and see if uptake increases as the plants establish themselves in a young tank, fwiw.

 

[hashbaz]

I have been considering the same thing, czcz. And with your confirmation, I will try it this week.

Thanks for the additional info.

 

[7Enigma]

czcz,

Just a tagalong question. I got the KNO3 from greg watson. Does this add ammonia to the water like hashbaz's calcium nitrAte? I'm hoping not since I did dose quite a bit recently (fortunately at my water change so hopefully if there was ammonia present the Prime took care of it). Thanks, and I'll be interested to see hashbaz's outcome, with that low bioload and that amount of light/plants, I would definately imagine you'd bottom out your nitrAtes pretty quickly. Do you have any nitrAtes in your tap water?

 

[czcz]

7Enigma, you're okay; KNO3 doesn't add ammonia.

Also very interested in what happens, hashbaz. Bookmarked your log

 

[jcarlilesiu]

for what its worth... i rarely see ANY drop in nitrates unless following a water change of course. I bought KNO3 expecting to dose and I have yet to have to. I run a constant 20 ppm of nitrate, in a heavily planted tank and it drops MAYBE 5 ppm over the course of the week. The tank is heavily planted, with very healthy growing and propogating plants, however I do have a pretty hefty bio-load. I have yet to see pearling...

 

[fish_4_all]

Same here, I rarely have to add KNO3 to my 10 gallon tank. Granted it does have a heavy bioload and only 1 huge red melon sword and a couple small java fern. I dose about 5 ppm every 3 weeks or so to keep it up. I only feed once a day also.

 

[hashbaz]

I believe my assumption about incorrect testing was incorrect. This assumption was based on the idea that my Nitrates were all being used up, and that I was getting a false reading of 10-15ppm Nitrate.

I have been adding 5ppm of nitrate every day for 4 days. This has made a noticeable increase in my Nitrate measurements - disproving my theory that Nitrates were bottoming out.

My tank has tons of growth, lots of pealing, slurps down CO2, and slurps down PO4 but not NO3. I would have figured that with the setup I have, I would have to add nitrates every day, but this is not the case.

I guess I should be happy that my nitrates will maintain themselves without my help. (at least for now).

 

[Apocalypse_Gold]

With a lot of new plants you probably have some significant die-off, so the plants are decomposing and releasing some extra nitrogen compounds.