Nitrates

[brendanwp]

I know there are tons of discussions on Nitrates and I read through a bunch of threads, but I couldn't find my answer. Background: 30 gallon tank, for movement I have 2 power heads and a pump so my flow is good. 3 small fish (clown, damsel, and a chromis) which were just added this week. My ammonia and nitrites are 0 and my PH and temp are fine. Did a 20% water change the day after I added the fish.

Question:
My Nitrates are very high...50+. Before and after my water change, which doesn't make sense. I will get to the store to get a new test kit this weekend, but what else could be causing the spike? I have a lot of critters (3 anemones, 3 brittle sea stars, 2 starfish, a decorator crab, 2 porcelain crabs, peppermint shrimp, various snails and hermits) and all seem to be doing well. The 3 fish seem fine as well, eating and everything. The shrimp even molted last week. One final note, I don't seem to have any algea bloom or growth.

thanks,

 

[CStrickland]

It sounds like you added three fish to an empty 30g? I would guess there was an ammonia spike that your biofilter processed into nitrates. In a new tank the bacteria that process nitrates populate slower, so they probably haven't caught up yet. My nitrate test gets kind of hard to read over 40 ppm, you may have had higher levels and the WC brought it down to 50. Assuming you are using rodi, or some nitrate-free source for your new water.

Water changes should help. I don't think it would be excessive to do 10% today and another 10% the day after tomorrow and see if that helps. But I wouldn't worry too much, 50ppm isnt hurting your fish IMHO.

 

[brendanwp]

No ran through the full cycle, 30 lbs of live sand, 60 lbs of live rock. But after search on the site today I think its because I have no changed out (or cleaned) my filter sponges. Going to do that tonight and see what happens.

 

[CStrickland]

Yeah, you need to clean those really often if you must use them and don't want nitrates

 

[brendanwp]

When you say "must use them", what happens if I just rely on the live rock? What benefits do I get from the sponges?

 

[3FordFamily]

When you say "must use them", what happens if I just rely on the live rock? What benefits do I get from the sponges?

Well sponges will give the beneficial bacteria needed in the complete nitrogen cycle a place to propagate and "attach" for lack of a better term.

Really, if you have a substrate and sufficient live rock I don't think you need a sponge, IMO.

 

[CStrickland]

They're really good at raising nitrates, if that's a benefit

The bacteria that convert ammo to nitrate love them because they use oxygen and "eat" ammonia. The poo and old food get caught in the netting / bioballs/ whatev, decay into ammo, and the bacteria can sit right there and work on it while the water flows through providing tons of oxygen. It's a buffet with a nice breeze.

The bacteria that rid your tank of nitrates do not like oxygen, so you get out of balance by creating a very good enviro for just one part of the cycle. But again, wouldn't worry about 50 ppm too much in a brand new tank that hasn't had many water changes. Just my opinion.

 

[bertoni]

I agree that sponges can cause an increase in the nitrate level. I'd probably remove them from the system one at a time, in case they're currently needed to process ammonia. Other common sources of nitrate include debris, often trapped in coarse substrates, and more food than the filtration can handle.

I'd probably start by removing the sponges and perhaps checking for debris traps, and give those changes some time to help. Water changes can lower the nitrate level, but it'll jump back up fairly quickly if there's an underlying problem.

 

[Dan_P]

They're really good at raising nitrates, if that's a benefit

The bacteria that convert ammo to nitrate love them because they use oxygen and "eat" ammonia. The poo and old food get caught in the netting / bioballs/ whatev, decay into ammo, and the bacteria can sit right there and work on it while the water flows through providing tons of oxygen. It's a buffet with a nice breeze.

The bacteria that rid your tank of nitrates do not like oxygen, so you get out of balance by creating a very good enviro for just one part of the cycle. But again, wouldn't worry about 50 ppm too much in a brand new tank that hasn't had many water changes. Just my opinion.

I am not following the logic here. When organic matter is not caught in a sponge or filter, it is scattered about the tank where it is digested by bacteria anyway. Seems like the same metabolic result, mineralized food and fecal matter ending up in the water column either way.

 

[bertoni]

The general thought is that the artificial media do not support denitrification well, and so dump nitrate into the water column. Live rock does support denitrification, and produces the nitrate in close proximity to denitrifying microbes, which encourage more complete denitrification. There are some discussions of this in the past, with at least one pointer to the literature that provides some support for this idea, but there's a lot of guessing involved.

 

[CStrickland]

I am not following the logic here. When organic matter is not caught in a sponge or filter, it is scattered about the tank where it is digested by bacteria anyway. Seems like the same metabolic result, mineralized food and fecal matter ending up in the water column either way.

Ideally it is carried to a skimmer, which removes it from the water column entirely. When it does float around and settle, it does so in places that have less flow (allowing it to sink because the force of gravity is greater than the force of the water current). Often it lands on some rock or sand and settles into a crevice with even slower movement of water. That lack of flow allows denitrifying (gets rid of nitrate) bacteria to colonize close to or under nitrifying (gets rid of ammonia) bacteria and thrive in water that has had the oxygen respirated out of it, maintaining a balanced cycle. High flow areas by their very design prevent the lower oxygen environment that the denitrifying bacteria require, so they encourage only the first part of the cycle (nitrification).

This is why people often see rapid resolution of high nitrates when they begin changing their filter socks every day or two, or start cleaning their sponges properly (or remove them altogether). When less food is trapped for the nitrifying bacteria, they do not over-populate and outpace the denitrifying bacteria so the cycle is balanced. Further, some media are hard to clean. Many media are sold as practically set-and-forget, unlike filter sock which are easily swapped. Since most do not practice this level of maintenance, these filters tend to raise nitrates.

ETA Bertoni's right, I'm speculating as to cause because the reduction in nitrates is common following removal of the media. The rock works if you let it. Also, IMO shallower sand beds are one explanation for the increase in high nitrate issues, as well as its just easy to test for. As I said, OP's is not a crazy level

 

[Dan_P]

The general thought is that the artificial media do not support denitrification well, and so dump nitrate into the water column. Live rock does support denitrification, and produces the nitrate in close proximity to denitrifying microbes, which encourage more complete denitrification. There are some discussions of this in the past, with at least one pointer to the literature that provides some support for this idea, but there's a lot of guessing involved.

I suppose you can invoke the proximity arguement for a sand bed as well.

There is probably something to the idea but it cannot be the entire story. You can use sponges and bioballs without having nitrate problems. So, there must be another factor or two that makes sponges look as though they produce nitrates.

The real story might just be a shift from a mixed heterotrophic-autotrophic biofilter that uses ammonia for proteins and oxidizes it for energy to one dominated by autotrophic bacteria that oxidizes a greater proportion of the ammonia to nitrate. The shift being a consequence of the biofilter becoming carbon limited. The role of the sponge and bioball might be a highly oxygenated surface which when removed, shifts the biofilter back to a more heterotrophic one.

 

[Dan_P]

Ideally it is carried to a skimmer, which removes it from the water column entirely. When it does float around and settle, it does so in places that have less flow (allowing it to sink because the force of gravity is greater than the force of the water current). Often it lands on some rock or sand and settles into a crevice with even slower movement of water. That lack of flow allows denitrifying (gets rid of nitrate) bacteria to colonize close to or under nitrifying (gets rid of ammonia) bacteria and thrive in water that has had the oxygen respirated out of it, maintaining a balanced cycle. High flow areas by their very design prevent the lower oxygen environment that the denitrifying bacteria require, so they encourage only the first part of the cycle (nitrification).

This is why people often see rapid resolution of high nitrates when they begin changing their filter socks every day or two, or start cleaning their sponges properly (or remove them altogether). When less food is trapped for the nitrifying bacteria, they do not over-populate and outpace the denitrifying bacteria so the cycle is balanced. Further, some media are hard to clean. Many media are sold as practically set-and-forget, unlike filter sock which are easily swapped. Since most do not practice this level of maintenance, these filters tend to raise nitrates.

ETA Bertoni's right, I'm speculating as to cause because the reduction in nitrates is common following removal of the media. The rock works if you let it. Also, IMO shallower sand beds are one explanation for the increase in high nitrate issues, as well as its just easy to test for. As I said, OP's is not a crazy level

Interseting angle except I have no live rock and a shallow sand bed and no detectable nitrates. I added a refugium recently to deal with phosphates. So, we have to rethink the notion of shallow bed equals nitrate issue.

The reduction of nitrate level after media removal is probably incompletely understood. Cleaning media just as likely removes ammonia oxidizing bacteria colonies as it does organic matter which everyone is blaming for elevated nitrates. Reducing the ammonia oxidizer population will leave more ammonia for other consumers like algae, cyanobacteria and heterotrophic bacteria, making the nitrate level decline. You could probably have dirty filter media if you carbon dose.

 

[CStrickland]

OP has 60# of rock in a 30g tank and had never cleaned their sponges.

I think it's interesting too, and I'd like to hear more about your tank, but maybe we should start a new thread for this?

 

[bertoni]

I suppose you can invoke the proximity arguement for a sand bed as well.

Definitely.

There is probably something to the idea but it cannot be the entire story. You can use sponges and bioballs without having nitrate problems. So, there must be another factor or two that makes sponges look as though they produce nitrates.

I don't see why it can't be the whole story, at least in some tanks. I think it's possible for some setups to denitrify all the nitrate from some sort of bio-ball or sponge setup.

The real story might just be a shift from a mixed heterotrophic-autotrophic biofilter that uses ammonia for proteins and oxidizes it for energy to one dominated by autotrophic bacteria that oxidizes a greater proportion of the ammonia to nitrate. The shift being a consequence of the biofilter becoming carbon limited. The role of the sponge and bioball might be a highly oxygenated surface which when removed, shifts the biofilter back to a more heterotrophic one.

This part doesn't make sense to me yet. I think that all of the ammonia is likely to be oxidized, at least at some point. That's how it's metabolized. An alga or plant might be able to take up ammonia directly, but that doesn't mean that it won't oxidize the ammonia. What does carbon limitation do? Autotrophic bacteria are likely to take up fixed nitrogen as part of photosynthesis.

 

[Dan_P]

OP has 60# of rock in a 30g tank and had never cleaned their sponges.

I think it's interesting too, and I'd like to hear more about your tank, but maybe we should start a new thread for this?

Agree, we are close to hijacking this thread. The set up is almost a year old, so, I could write a 1 year anniversary review of my Long Island Sound tidal zone aquarium experiment.

 

[Dan_P]

I don't see why it can't be the whole story, at least in some tanks. I think it's possible for some setups to denitrify all the nitrate from some sort of bio-ball or sponge setup.

Yes, there are hetertrophic bacterial that consume nitrates but we keep forgetting that ammonia is the preferred nitrogen source for many organisms. The organism is not required to reduce nitrate to ammonia before using it. Ammonia is a lower energy source of nitrogen and can even inhibit or slow down nitrate uptake. So, what appears to be denitrification can also be heterotrphic ammonia uptake or both. This shift from removing nitrogen as nitrate to nitrogen as ammonia is facilitated by carbon dosing.

This part doesn't make sense to me yet. I think that all of the ammonia is likely to be oxidized, at least at some point. That's how it's metabolized. An alga or plant might be able to take up ammonia directly, but that doesn't mean that it won't oxidize the ammonia. What does carbon limitation do? Autotrophic bacteria are likely to take up fixed nitrogen as part of photosynthesis.

Ammonia uptake is preferred because it can be used directly to make amino acids and then into proteins. So, not all ammonia is oxidized in nature or the aquarium.

The link with carbon limitation is that carbon is used both to build cells and to make energy, i.e., produce carbon dioxide. Because a portion of the available carbon is lost to CO2, the ratio of nitrogen to carbon increases. Recall the Redfield number. When this happens, hetertrophic organisms leave behind excess nitrogen when they take up carbon and nitrogen to build cells. With a deficit of carbon, the hetertroph has no need for this left over nitrogen. That's where autotrophic bacteria and algae come in to scoop it up because they use CO2 as their carbon source. What carbon dosing does is to rebalance the carbon to nitrogen ratio for the heterotrophs. Adding carbon encourages growth and that requires nitrogen. So, what looks like denitrification may in fact be the increased consumption of ammonia for bacterial growth before nitrate is even formed plus nitrate consumption.

I am working on a diagram that pulls all this together, showing the flows of carbon and nitrogen to the various type of "trophs" . Maybe I should finish it and start a new thread. I would like to line up some collaborators to review it before going live.

 

[brendanwp]

Tested the water last night, Ammonia was just over 0, nitrites - 0, and nitrates the same. This morning the water looked a little cloudy. I do think its going to take more then 24 hrs to see some change, but if the ammonia goes any higher tonight I will do small water change. All the life in the tank seems fine though, my rock anemone was bigger last night then I had ever seen it. Here is a pic of the tank the day before I got my first fish.

View attachment 306676

 

[CStrickland]

That's a pretty tank Brendan! Are the sponges real?

 

[brendanwp]

Thanks. Yes...all from Tampa Bay Saltwater.