An experiment in nitrate reduction

[dleute]

For a number of reasons, I decided to delay getting fish in my freshly cycled tank. It's at the point where I can dose janitor ammonia to 4ppm and reduce it to zero within a day (probably faster). Last 1ppm dose reduced ammonia to 0 in 3 hours (seneye). Didn't check nitrites at the time.

During the cycling process I had a bacteria bloom mostly on my rocks (slimy white hair looking stuff). I assume it's because phosphate was leaching from dry BRS pukani and it was the easiest place for it to grow. Well, all that stopped (or at least slowed down), phosphate reduced to 0.03 or less, and nitrates are high (currently 50-75ppm but were 100, though I'm not sure I trust the test), nitrites drop to 0 very quickly after an ammonia dose.

Since I'm holding off on fish, and there is no life at risk in the tank, I decided to experiment with what it would take to reduce nitrates through carbon dosing.

My tank is a 93 gallon cube with approximately 10-12 gallons active in the sump (it's a 20 gallon long tank acting as sump). So, I started dosing vinegar through my ATO (also kalk to prevent bacteria bloom in the ATO reservoir). I also add additional vinegar manually as my evaporation is quite low currently (added a cover in preparation for firefish that jump). Total amount of vinegar is approximately around 30-40ml a day, but unfortunately a bit of a guess due to ATO usage

Since my phosphates were so low, I needed a phosphate source (also removed my GFO reactor) to have enough phosphates for bacteria to consume phosphates and nitrates. I used 1 gram of pellet food which by my calculations should supply a phosphate level of 0.135 ppm in total as it decomposes. As if I was feeding a fully stocked tank. I also add a small bit more food every day, to make sure some phosphates remain available.

It took a few days but another bacteria bloom occurred. It looks like nitrates have dropped slightly but not much (possibly within the realm of user test error).

I am also continuing to dose much smaller amounts of ammonia to keep the cycle going. The food hasn't seemed to spike ammonia on its own (at all via seneye). I assume the process is slow enough that the nitrogen cycle is converting everything available very quickly.

So, I'm curios, can nitrates be reduced to zero via carbon dosing? And how long does it take? Or is the food I'm adding to provide the phosphates also providing too much nitrate (I assume it must add some)?

This experiment was inspired from reading this: http://www.advancedaquarist.com/2012/3/chemistry

And this:

http://reefkeeping.com/joomla/index...ar-dosing-methodology-for-the-marine-aquarium

Thoughts? Questions? Ideas? Results from your own experiments?

I am, unfortunately, not being quite as scientific as I should. I just have this cycled tank and no ability to put fish in it, so why not?

--Derrek

 

[bertoni]

Carbon dosing can reduce the nitrate level to zero (detected) in many tanks, but not all. In some cases, the process seems to be phosphorus-limited. In this situation, I would stop the ammonia dosing and do some water changes if I were worried about the nitrate level. Fish will be fine with 100 ppm, so you could ignore it. My guess is that the nitrate source is all that ammonia that's been added, so the water changes should help a lot, with some luck.

 

[dleute]

Carbon dosing can reduce the nitrate level to zero (detected) in many tanks, but not all. In some cases, the process seems to be phosphorus-limited. In this situation, I would stop the ammonia dosing and do some water changes if I were worried about the nitrate level. Fish will be fine with 100 ppm, so you could ignore it. My guess is that the nitrate source is all that ammonia that's been added, so the water changes should help a lot, with some luck.

I figured keeping the ammonia would make sure the cycle doesn't stall as I wait for fish. However, the food should do that as well. I assume I shouldn't stop both or I may have to re-cycle if I can't put fish in for several weeks?

It's not really something I need to fix (yet). I'm pretty happy with my tank cycle. It went pretty fast and seems to handle plenty of ammonia.

I can do water changes when I'm ready to put fish in. The point of the experiment was to see if I could get nitrates to reduce quickly without water changes. I know based on my schedule (one of the reasons I delayed putting fish in) that I may not always have time for water changes. In fact, I'm building an automatic water change system (with my apex) knowing this. It just won't be available for a few months.

This is my first tank, so I have no prior experience with reef chemistry. I'm just experimenting without risking actual fish.

Seeing the tank respond even without inhabitants is fascinating to me!

--Derrek

 

[bertoni]

Yes, adding a bit of fish food will help ensure that some of the bacteria stay alive. I'm not sure how much actually is needed, but probably not much.

If you want to try to reduce the nitrate without water changes, then some carbon dosing might be an interesting experiment. Vodka or vinegar would be fine.

 

[Cajunreefer87]

Following

 

[dleute]

Anyone aware of a more specific high nitrate test kit?

I think my nitrates are reducing rapidly, but when the range is 50-100 (salifert) it is hard to tell.

 

[bertoni]

I don't know of a high-range kit, but you could dilute the sample to give an approximation. I'd try 3:1 fresh saltwater to tank water as a starting point.

 

[dleute]

I don't know of a high-range kit, but you could dilute the sample to give an approximation. I'd try 3:1 fresh saltwater to tank water as a starting point.

That should work. So with salifert which requires 1ml of tank water, I would use 0.75ml of fresh saltwater and 0.25ml of tank water and run the test as usual?

I assume then I should get a quarter the measurement results on the salifert test and multiplying by 4 should put me in the same color range as 1ml of tank water?

Am I doing the math correctly?

Thanks!

--Derrek

 

[dleute]

I have a hard time reading colors, but it looked like a result of 10 on the color card which would be 40ppm if I did everything correctly.

I stupidly forgot to try the low range nitrate through the side. I'll try that tomorrow.

It does look like nitrates are dropping rapidly.

--Derrek

 

[bertoni]

The math is all correct. If you have trouble drawing .25 ml of water accurately, you could mix 3 ml of fresh saltwater and 1 ml of tank water, and discard all but 1 ml.

 

[dleute]

The math is all correct. If you have trouble drawing .25 ml of water accurately, you could mix 3 ml of fresh saltwater and 1 ml of tank water, and discard all but 1 ml.

Also good advice. I will use that method tomorrow as I believe it will be more accurate. Getting the 0.25ml with my syringe was probably good enough, but this would eliminate yet another source of user error. I like that.

A digital nitrate test would make me very happy. My digital alkalinity and phosphate checkers are much easier for me.

--Derrek

 

[dleute]

I used the 4ml 3:1 version tonight and had to use the more detailed scale. The thing that bothers me is the two scales on the salifert test had wildly different results.

Looking down I got 10 which should mean I'm down to 40ppm. But sideways, I got 50 which would correspond to 20ppm (50/10*4). It is possible the sideways one was optimistic. If it were 100, then both results were 40ppm which makes much more sense.

Interesting stuff. There is also a lot of stringy bacteria I'm having a hard time pulling out of the tank. I hope it detaches over time. The eheim vacuum won't suck it off rocks (it can get it off of the gravel). My 50 foot python hose never produces enough suction for anything. I haven't had time to do a regular siphon and a bucket yet.

Neat stuff. Tank parameters have been otherwise stable.

--Derrek

 

[WWIII]

Once upon a time i made the same mistake of dosing ammonia more than once, "to ensure the tank was cycled". My nitrates took almost a year to get to zero. This was in a 200 gallon tank, so lots of water changes, and lots of salt. $$$ I now try to recommend to anyone who asks to only dose ammonia once, twice max. The bacteria can live for a long time without a food source and a little fish food goes a long way. Hope you have luck getting them down faster than I.

 

[dleute]

Once upon a time i made the same mistake of dosing ammonia more than once, "to ensure the tank was cycled". My nitrates took almost a year to get to zero. This was in a 200 gallon tank, so lots of water changes, and lots of salt. $$$ I now try to recommend to anyone who asks to only dose ammonia once, twice max. The bacteria can live for a long time without a food source and a little fish food goes a long way. Hope you have luck getting them down faster than I.

How high were they? How much ammonia and what concentration did you dose? Right now, the nitrates don't seem like a particular challenge. Carbon dosing vinegar and adding small amounts of phosphate from food seem to be doing it pretty quickly.

In my case, once I saw that nitrites were being processed, I only used small doses of ammonia every few days (1-3ml 10% ace janitor ammonia which barely took my tank to 1ppm usually 0.8 or 0.6). Nitrates had already started to drop on their own, I just wanted to help them along.

Nitrites did stay off the scale for weeks (my test only goes to 5.0 ppm), but they dropped to 0 and stayed there and of course that's when the nitrates spiked to 100ppm. Now at 40ppm with no ammonia dose (and will never be another one).

What I don't know is how all this compares to the relative bio-load of ammonia and nitrates from fish. Did my larger doses of ammonia simulate a full bio-load? I have no idea.

--Derrek

 

[bertoni]

I think your doses simulated an extremely heavy bio-load, maybe an infeasible one. That's one reason the nitrate level was so high. 1 ppm of ammonia converts to about 3.6 ppm of nitrate.

 

[WWIII]

I used the same 10% ammonia from hardware store. Dosed to 4ppm the first time. Then dosed 2 times to 2ppm. Then finally dosed to 1ppm the last time. My nitrates were never higher than 50ppm. I was able to get them down to 20ppm rather quickly. Within the first couple water changes. Then to get from 20ppm down to 0 took about 10 months after that. I probably did 20 water changes of 20% roughly in that time, as well as a couple weeks doing larger percentage water changes a couple days apart. Then started dosing vinegar daily and doing 20% water changes every 2 weeks. Finally, after about 3 months of dosing and water changes I was able to get them down to zero.

In a smaller tank I would think it would be much easier, but in my 200 gallon (around 250 gallons total volume) it's just a lot of water to change out once nitrates get that high. The tank was lightly stocked this entire time (after the cycle of course) so i don't believe the fish were adding too much to the issue.

All I can say is to get nitrates from around 20ppm to zero was a pain and took a lot of patience and diligence. Like they say, every tank is different, but this was my experience. It's not necessary to feed the bacteria "pure" ammonia to keep them alive and it will only end up as nitrates, which is why i recommend to dose as little as possible.

Sounds like you have, and are, doing the right research! There are plenty of ways to start a tank and manage it along the way. Plenty of opinions out there as well! Let us know how it goes for you.

 

[dleute]

I think your doses simulated an extremely heavy bio-load, maybe an infeasible one. That's one reason the nitrate level was so high. 1 ppm of ammonia converts to about 3.6 ppm of nitrate.

Well, that math works out nicely. 100ppm was the high point, and by my graph history, that is representative of 27ppm dosed ammonia over 5 weeks (approximate, however as it processed ammonia faster, the spikes don't actually capture the highest point of each dose spike. so the later spikes probably represent a higher ppm than they appear to show on seneye). That math is almost too perfect working out to 97.2ppm nitrates added from ammonia alone. My gutt feel is it would be closer to 130ppm nitrates in reality especially since I watched nitrates dip slightly a few times.

I'm sure some nitrates came off other things. I would assume dry rock adds some nitrates. Etc.

All good to know. I'm very happy with my tank. I just wish it were easier to get rid of this bacteria. I'll get more and more of it through normal maintenance.

--Derrek

 

[dleute]

I used the same 10% ammonia from hardware store. Dosed to 4ppm the first time. Then dosed 2 times to 2ppm. Then finally dosed to 1ppm the last time. My nitrates were never higher than 50ppm. I was able to get them down to 20ppm rather quickly. Within the first couple water changes. Then to get from 20ppm down to 0 took about 10 months after that. I probably did 20 water changes of 20% roughly in that time, as well as a couple weeks doing larger percentage water changes a couple days apart. Then started dosing vinegar daily and doing 20% water changes every 2 weeks. Finally, after about 3 months of dosing and water changes I was able to get them down to zero.

In a smaller tank I would think it would be much easier, but in my 200 gallon (around 250 gallons total volume) it's just a lot of water to change out once nitrates get that high. The tank was lightly stocked this entire time (after the cycle of course) so i don't believe the fish were adding too much to the issue.

All I can say is to get nitrates from around 20ppm to zero was a pain and took a lot of patience and diligence. Like they say, every tank is different, but this was my experience. It's not necessary to feed the bacteria "pure" ammonia to keep them alive and it will only end up as nitrates, which is why i recommend to dose as little as possible.

Sounds like you have, and are, doing the right research! There are plenty of ways to start a tank and manage it along the way. Plenty of opinions out there as well! Let us know how it goes for you.

Good to know. I have not done a true water change yet. I replaced some I pulled out vaccuming, but probably not 10% total. I also let my ATO re-fill some of that when my salinity was a bit high and ph a bit low (kalk in the ATO which I primarily did to dose vinegar from the ATO).

I may face the same challenge for 20ppm nitrates. We will see. I'm ok with things going slowly. I am using marine pure since day 1. Not sure if it does as it claims, but I have seen nitrate reductions and a fairly quick cycle (based on my research). Maybe that helped. I don't know what other media you are using. I was running GFO (but stopped it as I need phosphates currently for bacteria to consume nitrates) and I haven't started the carbon yet.

I was thinking of going zeovit. But honestly, all the added expense for reactors (and automating it, because I can't be there every single day) just talked me out of it for now. I also decided I really need to understand what is going on. And starting simpler and learning (perhaps the hard way) will be better in the end.

It's really gratifying to make changes intended to create a bacteria bloom and reduce nitrates, and actually see it happen. As opposed to starting full zeovit and never see anything but perfect parameters. When I understand what each zeovit thing is really doing, maybe then I'll try it.

I got off on a tangent. I'm really enjoying this hobby.

--Derrek

 

[dleute]

I've been reading some more on nitrate, phosphate and carbon. Specifically I am learning more about the redfield ratio.

WWIII, some questions:

It is interesting to me that you ran into issues at 20ppm nitrate. Were you tracking phosphate at the time as well?

Did you have any algae outbreaks once you reached that 20ppm nitrates? I would bet yes, particularly of the green variety. The logic is below.

My phosphate has not gone above 0.03 (not since the cycle took hold) despite me adding what should be about 0.315ppm phosphate via pellet food in the first feeding (incredibly, that is just 1 gram of food). However, I have seen bacteria bloom and reductions in nitrate.

A month ago I had a phosphate measurement of 0.31, then 0.15 then 0 (over the course of a week). This I believe is when my first bacteria bloom began, but at the time, I didn't know it was a bacteria bloom and thought it was some kind of algae. I then started gfo thinking it was an algae bloom. That likely reduced my phosphates to 0 (none were being added outside of potential dry rock leaching) quickly and stopped any chance of algae and additional bacteria blooms. It also let my nitrates run wild as nothing could consume them without phosphate.

If the redfield ratio of 106:16:1 carbon, nitrates and phosphates is a "healthy" environment, then my tank should be sprouting green hair algae in crazy amounts. However, I don't see any (or any other type of green algae).

My assumption at this time is the bacteria is out competing consuming phosphates and nitrates (especially since it is strongly visually dominant). And that even if hair algae largely needs nitrates, it must need some phosphates to grow. Right now, bacteria wins in my tank.

My guess, as I get closer to the redfield ratio, green nitrate thriving algae will start to appear. The phosphates will be abundant enough to feed algae along with the bacteria. And having this start at 20ppm nitrates makes a lot of sense. Algae consumes nitrates but also becomes a source of it as it dies. Bacteria (as far as I know) does not (I would love more info on this). Hence it's now harder to drop below 20ppm nitrates as the nitrates you have are being converted into more nitrates instead of removed by water changes and/or the skimmer.

So, my goal for now, is to keep the bacteria in control. And hope I can zoom through the 20ppm barrier by pushing a 16:1 ratio (then hopefully reducing both at that ratio, which will be hard to do since phosphates are quickly consumed and not measured).

I hope all that makes sense and I'm not entirely in left field.

--Derrek

 

[tmz]

A few things fyi:

I agree the ammonia likely caused the nitrate via chemoautotrophic ammonia oxidizing bacterial activity converting it to both to nitrite and then nitrate.

Denitrication via the normal cycle requires anaerobic ( low oxygen availability) activity , usually occurring in substrate or pores of live rock where oxygen rich water is very limited given low flow in these areas. Obviously ,this requires adequate surface areas exposed to hypoxic (low to no oxygen) bearing water. It can take time for the denitrifying bacteria to establish themselves in these areas where they reduce the nitrate (NO3) to N by taking oxygen from it when free oxygen is unavailable leaving some of the remaining N to bind with N forming N2 ,nitrogen gas which bubbles out of the tank retunign the nitrogen to the atmosphere . More porous surface area can help increase the anerobic activity.

Carbon dosing feeds heterotrophic bacteria which primarily take the N (nitrogen ) from ammonia directly in a one step process without adding nitrate.In essence reducing the amount of new nitrate in the system. They also use some nitrate, phosphate and other elements) . It can take months for nitrate present at the start of carbon dosing to be reduced. They can also reduce the ammonia oxidizing bacteria in play by outcompeting them for ammonia. The 40ml 5% acetic acid vinegar dose for ca. 100gallons is moderate ,IMO.