Why are nitrates rising overnight?

I’m at the end of cycling my tank using the fishless method. (Both ammonia and nitrites dosed at 2ppm drop to zero after about 8 hours).

Yesterday I did two 75% water changes in the 75 gallon to get nitrates below 5ppm to get ready to add fish. After the second change nitrates were 5ppm.

Since last night nitrates have risen to 20ppm. There are no nitrates in my tap water so why the big rise?

I have a planted tank with fast growers (planted about 4 days ago) and I have a very large piece of driftwood. I’m also seeing a couple of small patches of white fungus on the substrate (bdbs) and on the driftwood.

Any ideas why the nitrate jumped?

 

You say that there are small patches of white fungus on the substrate.

That tells me there is something rotting in there. Fungus will only grow on sources of nutrients, that usually being decaying organic matter. Have you had an algae outbreak that you killed with chemicals?

The only other explanation is that something fell in there, drowned and then began rotting, leading to what's happening now.

EDIT: Have any of the plants shed leaves or branches?

 

the driftwood is very soft and bits have come off it. I’ve removed it to see if the nitrates stabilize. I also have a few leaves from the newly planted plants which I scoop out every day.

 

I’m at the end of cycling my tank using the fishless method. (Both ammonia and nitrites dosed at 2ppm drop to zero after about 8 hours).

Yesterday I did two 75% water changes in the 75 gallon to get nitrates below 5ppm to get ready to add fish. After the second change nitrates were 5ppm.

Since last night nitrates have risen to 20ppm. There are no nitrates in my tap water so why the big rise?

I have a planted tank with fast growers (planted about 4 days ago) and I have a very large piece of driftwood. I’m also seeing a couple of small patches of white fungus on the substrate (bdbs) and on the driftwood.

Any ideas why the nitrate jumped?

Hello lisa...

For one, nitrates are at the end of the nitrogen cycle, so 20 ppm is really nothing to worry about. The rise is likely because your aquatic plants rest when the tank lights are out. So, they aren't using the nitrates as much. As long as you follow a sound water change routine, you'll have no tank problems. Fungus is pretty normal, it grows in cracks and crevices in the wood, where small bits of food fall. Ramshorn snails will take care of this little problem.

Old

 

the driftwood is very soft and bits have come off it. I’ve removed it to see if the nitrates stabilize. I also have a few leaves from the newly planted plants which I scoop out every day.

I don't think it's the driftwood causing it; usually, driftwood will lower pH if it starts rotting. I haven't heard of driftwood causing nitrate emissions.

If you're taking shed leaves out of the tank, they aren't causing it.

Something in there is definitely releasing a lot of ammonia which is being converted into nitrate. Is it possible that with your plants or driftwood, you've accidentally brought some pond snails along? Pond snails are basically the E. colI of the fishkeeping world: in low amounts they can be neutral or even good, but they breed like rabbits and can cause serious problems in high numbers. In other words, you aren't missing out on anything if you don't have them.

I'm thinking that you've brought in a small group of pond snails with your plants, they've died during the cycling process and now they are rotting somewhere. If you have bright sand, dead shells can be hard to find since they will blend in so well. If you have gravel then good luck finding snail corpses to remove. Anyway, I think I've scared you enough

If it's not snails, the only other thing I can think of is some sort of spider, insect or terrestrial gastropod has accidentally fallen in, drowned and is now rotting somewhere. No fishless tank produces 15ppm of nitrate in not even 24 hours, especially with fast growing plants that actively eat nitrate. 75 gallon tanks are big and an unwanted organism can be hard or almost impossible to find.

Hello lisa...

For one, nitrates are at the end of the nitrogen cycle, so 20 ppm is really nothing to worry about. The rise is likely because your aquatic plants rest when the tank lights are out. So, they aren't using the nitrates as much. As long as you follow a sound water change routine. You'll have no tank problems. Fungus is pretty normal, it grows in cracks and crevices in the wood, where small bits of food fall. Ramshorn snails will take care of this little problem.

Old

...no fishless tank produces 15ppm of nitrate overnight. Something has to be producing that.

Also, no, macroscopic fungus is not a normal part of any tank. I'm pretty lax with cleaning my tank and very liberal with food yet I have zero noticeable fungus growth. If fungus is growing into a macroscopic colony, there's rotting food (overfeeding) or something's dead.

 

...no fishless tank produces 15ppm of nitrate overnight. Something has to be producing that.

Hello Cry...

No fish, so no problem. This could easily be an error in testing too. 15 ppm nitrates is a great reading for any tank.

Old

 

Hello Cry...

No fish, so no problem. This could easily be an error in testing too. 15 ppm nitrates is a great reading for any tank.

Old

Didn't think about that to be fair.

OP, what test kit are you using?

 

Old is correct. Plants sleeping nitrates rising. Your cycle is still producing nitrates. Last stage of the cycle. 20ppm is fine. Test again at the end of the day and see what you get. The white fungus happens to new driftwood. Some fish will eat it. How many plants do you have? Picture of tank would be good . What do you plan to stock the tank with?

 

Old is correct. Plants sleeping nitrates rising. Your cycle is still producing nitrates. Last stage of the cycle. 20ppm is fine. Test again at the end of the day and see what you get. The white fungus happens to new driftwood. Some fish will eat it. How many plants do you have? Picture of tank would be good . What do you plan to stock the tank with?

How do you suggest a fishless tank produces 15ppm of nitrate in less than 24 hours ignoring the possibility that it's an incorrect reading?

 

Ok I’ve never done a fishless cycle. Op is adding 2ppm of ammonia. So it’s the ammonia breaking down that is becoming the nitrate. I also don’t know how many plants are involved. The more plants the more nitrate being used during the day. Usually a incorrect nitrate reading is from not shaking the bottles enough. That reading is allways low to no nitrates. So I think the test is being done correctly. All in all 20 ppm of nitrate is no problem. If it’s going up 20 ppm a day (20 to 40 to 60) that would be a problem. Even snails won’t raise your nitrate that high.

 

Ok I’ve never done a fishless cycle. Op is adding 2ppm of ammonia. So it’s the ammonia breaking down that is becoming the nitrate. I also don’t know how many plants are involved. The more plants the more nitrate being used during the day. Usually a incorrect nitrate reading is from not shaking the bottles enough. That reading is allways low to no nitrates. So I think the test is being done correctly. All in all 20 ppm of nitrate is no problem. If it’s going up 20 ppm a day (20 to 40 to 60) that would be a problem. Even snails won’t raise your nitrate that high.

Completely agree, which is why I'm questioning it. 15ppm or even more at this point per day is a ridiculous nitrate emission

 

Hello lisa...

For one, nitrates are at the end of the nitrogen cycle, so 20 ppm is really nothing to worry about. The rise is likely because your aquatic plants rest when the tank lights are out. So, they aren't using the nitrates as much. As long as you follow a sound water change routine. You'll have no tank problems. Fungus is pretty normal, it grows in cracks and crevices in the wood, where small bits of food fall. Ramshorn snails will take care of this little problem.

Old

Agree. If you still add ammonia it is quite logical those end up in nitrates.
Same would have happened during the day.

 

How do you suggest a fishless tank produces 15ppm of nitrate in less than 24 hours ignoring the possibility that it's an incorrect reading?

Hello...

Fish in or fishless cycling you have an ammonia source. Ammonia mixed with the surround air begins to grow the bacteria that uses this form of nitrogen. That bacteria produces nitrite and grows the bacteria that uses it. That bacteria produces nitrate. Nitrate is used by the plants, mostly during the daylight hours. When dusk or night time begins, the plants rest. So, nitrate use is slowed. The fish, even at rest will produce waste and bacteria works 24/7 to break it down. Since the plants are essentially sleeping, nitrate will rise a bit.

Old

 

Completely agree, which is why I'm questioning it. 15ppm or even more at this point per day is a ridiculous nitrate emission

If 15 ppm were being produced every day, the nitrate level would rise accordingly. After 3 days nitrates would be at 45 after 6 days, 90 ppm. There is no problem if the nitrates are staying at 15 to 20. They aren't going away on their own and they will increase slightly as any organic material in the tank continues to decompose (plant cells, detritus from plants, insects, residual ammonia in substrate, microscopic organisms like molds, yeast, bacteria etc.) There is no mystery here. The OP dosed with ammonia, that ammonia was processed as bacteria had access to it. Ammonia continues to be produced in a tank containing organic material. Unless Nitrates continue to be produced at an exponential rate, this tank is behaving like cycled tank.

 

Here is my tank. I removed the driftwood this morning and put it in the bathtub. I’m going to leave there until it finally stops floating.


The tank is fully cycled. It processes 2ppm of ammonia, and the resulting nitrites, in under 8 hours. I’m using an API master test kit. I’ve used it so much it feels like it’s become a second job.

I added the plants about 4 days ago and have been trimming the melting leaves. The hornwort is growing like crazy and the rest are establishing nicely.

I have been continuing to add 2ppm of ammonia 2x/day since I don’t yet have fish or snails. And I just read here that 2ppm of ammonia creates 4ppm of nitrites, which creates 8ppm of nitrates. If I dose 2x/day there is the 15(16) ppm of nitrates.

Am I understanding that correctly?

The fish I’m planning are 3 or 4 angel fish, 10 kuhlI loach, a bristlenose pleco, a school of silver tip tetras, and a school of sterbaI cory cats.

Planning on Juvenile angels so they grow up with the others. If I have problem or end up with a breeding pair of angels I have a backup tank they can go to.

 

Here is my tank. I removed the driftwood this morning and put it in the bathtub. I’m going to leave there until it finally stops floating.
View attachment 629350
The tank is fully cycled. It processes 2ppm of ammonia, and the resulting nitrites, in under 8 hours. I’m using an API master test kit. I’ve used it so much it feels like it’s become a second job.

I added the plants about 4 days ago and have been trimming the melting leaves. The hornwort is growing like crazy and the rest are establishing nicely.

I have been continuing to add 2ppm of ammonia 2x/day since I don’t yet have fish or snails. And I just read here that 2ppm of ammonia creates 4ppm of nitrites, which creates 8ppm of nitrates. If I dose 2x/day there is the 15(16) ppm of nitrates.

Am I understanding that correctly?

The fish I’m planning are 3 or 4 angel fish, 10 kuhlI loach, a bristlenose pleco, a school of silver tip tetras, and a school of sterbaI cory cats.

Planning on Juvenile angels so they grow up with the others. If I have problem or end up with a breeding pair of angels I have a backup tank they can go to.

1 ppm ammonia = ~2.7 ppm nitrites
1ppm ammonia = ~3.6 ppm nitrates

You don't need your tank to process 4 ppm ammonia a day unless you are going to over stock your tank with pirahnas, 2ppm is way more than enough for a slightly overstocked tank.
As a matter of fact you don't even need to dose your tank to 2 ppm anymore, 1 ppm would be plenty until the day before you put your fish in there.

 

Thanks mom for the explanation. I’m stocking the tank today and I believe it will be under stocked by about 10-15 percent.

The lfs that I’m going to is a mom and pop with a super reputation so I’ll get their advice since my stocking list came from AqAdviser and I’ve recently learned it isn’t accurate.

 

Nice Thread! Thanks to all for the very educational discussion.

 

I'm still confused. How has 2ppm of ammonia become 15ppm of nitrate in 24 hours? Did you add in more ammonia?

Also, I know how the cycle works, I have a tank that has been established for 2 years. I'm questioning how that reading has come up.

 

It didn’t. The nitrates went up overnight because the plants were asleep so weren’t using nitrates. I tested last night and the nitrates had dropped back to 5ppm.

Tested again this morning and it confirmed that nitrates rise overnight then drop again by the end of the day.

 

That is interesting that plants would consume that much nitrate during the day. I had no idea they could consume that much.

 

Other than water changes plants are one of the few ways to remove nitrates. The other way is denitrifying bacteria. This way needs a dedicated filter filled with a pourous material. These bacteria grow in dark oxygen free areas and take about 2-3 months to develop. Best way to remove nitrate is water changes.

 

That is interesting that plants would consume that much nitrate during the day. I had no idea they could consume that much.

The number of plants she has don't consume 15 ppm nitrates in a day. Not even close. It's just nitrate levels tend to be higher in the morning and lower in the evening. Niitrate levels will continue to rise in the presence of organic material as long as that organic material is being broken down.

 

Is there a time of the day that is best to test water?

 

Is there a time of the day that is best to test water?

Test it in the morning when nitrates are at their highest, potentially toxic level. Adjust water change volume, frequency based on that.

 

That makes sense.