20 Gallon Tank Nitrate Dosing Journal

[gaberosenfield]

Like the tanks of many people who carbon dose, my aquarium has reached a point at which nitrates are undetectable (by my crappy API test kit) yet phosphates are very slowly rising (now at somewhere between 0 and 0.25 ppm). After reading up about it, I have decided to try nitrate dosing, in the hopes that my carbon dosing and skimming and macro algae growth will increase phosphate export. I have been using a small amounts of GFO, but I would prefer not to have to use any media and I have a few concerns about iron leaching into the tank. Anyway, I hope my experiences help others!

 

My first dose of KNO3 was today after a 20% water change (I do 10-20% weekly water changes).

 

I purchased 5 lbs of KNO3 off of a chemistry supply site years ago for some other projects. It is 99.999% pure (according to the seller). My system volume is somewhere between 20-25 gallons (an ~18 gallon tank with a 10 gallon sump + rock, sand, coral, etc...). I wanted to make a stock KNO3 solution that would be really easy to measure out and dose in my system, so I made a solution that will raise the concentration of nitrate in a 20 gallon system by 1 ppm when dosed with 1 mL. The following summarizes the simple calculations I did to make this solution:

 

1 ppm = 1 mg/L. 20 gallons = ~75 L. So 1 ppm in my system is 75mg. I wanted to make a solution that contains 75 mg nitrate per mL. 1 mole of KNO3 weighs ~101.1 g, of which only ~ 62 g is nitrate (the other ~39.1 g is potassium).

Setting up the claculation: (101.1 g KNO3 / 62 g NO3-) = (X mg KNO3 / 75 mg NO3-)

Solving for X by multiplying both sides by 75 mg NO3-: X = ~122.3 mg KNO3.

 

So I needed to make a solution that contains 122.3 mg KNO3 / mL. I decided to make 1 L. So, multiplying the top and bottom of this ratio by 1000, I needed to add 122.3 g KNO3 to 1 L of DI H2O. I used a balance to measure out 122.3 g KNO3 and added it to a 1 L bottle. Then I filled it up to the top with DI H2O. Just a side not for anyone who tries this: the bottle will get quite cold after you add the water because the solvation of KNO3 is endothermic! Anyway, after the solution cleared up, it was ready to dose.

 

For the first day, I decided to start really slowly. I added only 1 mL of my stock KNO3 solution, which should increase my tank's nitrate concentration by 1 ppm. Today's water parameters (before the water change) were: carbonate = 10 dKH, calcium = 400 ppm, nitrates = 0 ppm, phosphates = between 0 and 0.25 ppm. I did not measure the parameters after the water change, but I will start the rigorous recording procedure tomorrow.

[gaberosenfield]

Nitrates = 0 ppm today, phosphates = between 0 and 0.25. I dosed 1.1 mL of KNO3 solution today. No visible effects on tank, as expected.

[gaberosenfield]

Nitrates = 0 ppm, phosphates between 0 and 0.25. I dosed 1.2 mL of KNO3 solution today, targeting 1.2 ppm nitrate. No visible effects on tank, as expected.

[uglyfish]

Nitrate dosing is kind of cool because it's counterintuitive. The API phosphate test may be a bit coarse - I would try another test kit. Somewhere between 0 and 0.25 is too wide of a range. Algae can grow at 0.06.

 

What are you using as carbon source? I read VSV in another post, what ratio? How much carbon source?

How old is the tank? If you're running gfo - why do you think your phosphate is high?

 

If you add 1ppm nitrate - within 30 minutes, your nitrate test should show it. You said you added, but didn't detect it... are you testing the next day or immediately after adding?

[gaberosenfield]

Nitrates = 0 ppm, phosphates = between 0 and 0.25 ppm. Dosed 1.3 mL KNO3 solution today, targeting 1.3 ppm nitrate. No visible effects on tank.

[gaberosenfield]

Nitrate dosing is kind of cool because it's counterintuitive. The API phosphate test may be a bit coarse - I would try another test kit. Somewhere between 0 and 0.25 is too wide of a range. Algae can grow at 0.06.

 

What are you using as carbon source? I read VSV in another post, what ratio? How much carbon source?

How old is the tank? If you're running gfo - why do you think your phosphate is high?

 

If you add 1ppm nitrate - within 30 minutes, your nitrate test should show it. You said you added, but didn't detect it... are you testing the next day or immediately after adding?

I totally agree that the API test is WAAAY too coarse to measure phosphate in my system. I am planning on getting a hanna checker after the holiday (hoping that I can find a good deal somewhere after the christmas rush). For now, I am using what I have though, which is admittedly pretty crappy.

 

I am using my own VSV mix. It is equal parts by volume saturated dextrose solution, vodka, white vinegar that has been neutralized with excess sodium bicarbonate, and Seachem Reef Plus vitamin and amino acid supplement. I dose about 2 mL each morning, a maintenance level I have determined by trial an error dosing the maximum amount that does not cause bacterial biofilms to develop. I have been dosing this mix for about 4 months, and it has effectively lowered my nitrates and phosphates significantly, as well as drastically improved the growth and appearance of my SPS (and basically halted the growth of all my softies!).

 

Although my current tank has technically only been set up for 7 months, all the rock, most of the equipment, and some of the inhabitants have been in an aquarium in my possession for almost a year. The reason I switched tanks is that my first tank was just a disaster. I had no idea what I was doing and as a result, algae issues and nutrient levels were just impossible for me to properly combat. To make matter worse, I hadn't planned out my setup well at all, which made proper maintenance exceedingly difficult. I decided to just start over with a new tank.

 

Although I am using GFO, I do not currently have a reactor for it, so I'm sure it is not working as efficiently as it should be. My theory as to why I am having such a difficult time lowering phosphates is 2 fold. 1: All my rock is from my old nutrient rich set up, and is probably continuing to leach phosphates into my current tank. 2: My guess is that my carbon dosing and skimming, as well as mild macro growth and pruning, is removing nitrate and phosphate in a different ratio that the food I feed is adding. This creates an imbalance that in nutrient levels, leading to a nitrate limiting system.

 

These are just my guesses. In truth I have no hard evidence to back up any of my claims. This is not truly a rigorous experiment, it is just my experience with nitrate dosing that I am documenting here for the benefit of myself and others. Thanks for the question and sorry for the long response!

[gaberosenfield]

I realized there was one more question I didn't answer. I am not testing my water for nitrates after the dosing. I am only testing in the evenings right before the day's nitrate dose. So I expect it to be zero every time. I guess I should start testing after dosing just to make sure my targeted nitrate levels are approximately reached, and that my KNO3 solution was properly made... I was just too stingy to do that in the beginning... I will start doing testing post nitrate dosing tomorrow!

[uglyfish]

I realized there was one more question I didn't answer. I am not testing my water for nitrates after the dosing. I am only testing in the evenings right before the day's nitrate dose. So I expect it to be zero every time. I guess I should start testing after dosing just to make sure my targeted nitrate levels are approximately reached, and that my KNO3 solution was properly made... I was just too stingy to do that in the beginning... I will start doing testing post nitrate dosing tomorrow!

 

Always interesting to see experimentation... How much VSV solution are you adding? Are you increasing the VSV dosage in proportion with the KNO3 dose?

[gaberosenfield]

I have been adding about 2 mL per day (roughly 0.1 mL per gallon of water volume). I have not yet increased the VSV dosage, but I will if I see my nitrate levels not decreasing back to zero 24 hours after KNO3 dosing.

 

But I have some terrible news for this journal... My API Test kit appears to be even more useless than I thought!

 

Today I took your advice, uglyfish, and I measured phosphate and nitrate before KNO3 dosing and an hour afterwards. I also decided to measure the nitrates and phosphates in my freshly mixed saltwater. The results make me feel like trashing my test kit entirely.

 

Before dosing: Nitrate = 0 ppm, Phosphate = between 0 and 0.25 ppm.

 

One hour after dosing 1.4 mL KNO3 solution (targeting 1.4 ppm nitrate): Nitrate = ~0 ppm (maybe a tiny bit more? I'm not really sure...), Phosphate = between 0 and 0.25 ppm.

 

Freshly mixed saltwater: Nitrate = 0 ppm, Phosphate = between 0 and 0.25 ppm.

 

I only use RO/DI water from the lab in which I work in my tank. It is constantly monitored by an industrial TDS meter and I feel confident that it has virtually undetectable nitrates and phosphates. I will make a note of the TDS meter reading tomorrow when I go in.

 

If my DI water is good, there are only two other explanations I can come up with to explain these results.

Either the test kit doesn't work worth a crap, or my tank water actually has basically 0 phosphates and my KNO3 solution does not appreciably raise my tanks nitrate levels in an hour. I do not believe the latter explanation. I will take a water sample to my LFS for a water test this weekend. I will also be investing in a hanna checker for phosphates ASAP. Too bad they don't make one for nitrates too... Anyone have some good suggestions for a low range (say 0 to 5 ppm or so) nitrate test? Something easy to read!

[uglyfish]

Anyone have some good suggestions for a low range (say 0 to 5 ppm or so) nitrate test? Something easy to read!

 

Salifert or Red Sea Algae Control Test Kit

[gaberosenfield]

Well, because I will be out of town off an on for the next month, and because my test kit sucks, I will not post here in this journal for a while. By mid January I will have purchased a low range phosphate hanna checker and probably the red sea nitrate pro test kit (thanks for the suggestion uglyfish!). Then I will resume the experiment and post the results here.

 

On a side note, I think I may continue to dose a mL or so of KNO3 solution to my tank daily when I am home because I have actually noticed that my crocea clam and all my LPS seem a little happier since I began dosing. I'm not that surprised; many people claim that LPS and clams prefer a little nitrates in their water. My SPS seem unaffected, at least in terms of polyp extension and color (it obviously hasn't been long enough to notice any changes in growth rate).

[gaberosenfield]

My SPS seem unaffected, at least in terms of polyp extension and color (it obviously hasn't been long enough to notice any changes in growth rate).

 

Scratch that...although most of my SPS seem perfectly happy, my green pavona is losing color rapidly and my purple Montipora digitata is STNing...I didn't realize it at first, but today I see it has lost all the tissue at its base. It is just a 2-3 inch frag, and its polyps are still fully extended. Not sure if this is the result of nitrate dosing, a drop in calcium (I'm not sure how that happened...) or slightly decreased flow (I had to turn down my mp10 a bit cause it was causing salt creep to seep up over the edges of my tank). I moved the digi into higher flow and I will not keep dosing nitrates until I am satisfied that I have a good test kit.

[ZephNYC]

I'm not that surprised; many people claim that LPS and clams prefer a little nitrates

 

The clams do, or they will eventually die. I dose sodium nitrate for clams and maintain it at 1 ppm, and sps are even growing a little faster.