Stalled Cycle – My Nitrites Aren’t Dropping After Cycling My Marine Aquarium? - A Helping Hand

Welcome to Simple Reefs. This is a brand new website dedicated to taking the complexity out of Marine Aquarium Ownership. Our goal is to show you how you can own your very own slice of the ocean without spending a fortune. As well as giving you tons of easy to digest information on all things marine. We are still talking about stalled cycles and, today, we are discussing a situation which many of you may face when you nitrites aren’t dropping after cycling your marine aquarium.

We have really been going into all the ins and outs of stalled cycles in marine aquariums. After all, they are immensely frustrating. You just want to add fish to your tank and finally enter the world of reefs and coral but that damn nitrogen cycle just won’t finish.

You are testing your ammonia every day and the levels are doing great. Your aquarium can process 2PPM of ammonia in under 24 hours but those nitrites are staying high and they just won’t seem to drop. It’s enough to make you want to throw the towel in and quit. But why won’t the nitrite levels in your aquarium drop? Well, to understand that we first need to look at the nitrogen cycle itself.

How The Nitrogen Cycle Works

We talked about cycling a marine aquarium in our opening article on this subject. You are already at the point of seeing nitrites in your aquarium so, by now, you are aware of what the process entails. As well as the importance of the nitrogen cycle (Wikipedia Article) to a healthy marine aquarium.

To complete the nitrogen cycle, we are establishing a bacterial profile, in our tanks, that can process harmful compounds like ammonia. Eventually converting it into the less harmful compounds nitrite and nitrate. Without the presence of these nitrifying bacteria, ammonia would accumulate and poison our aquarium’s residents.

To accomplish this, we are adding ammonia to our aquariums every day. The ammonia will be converted into a compound called nitrite by a type of bacteria known as Nitrosomonas. These nitrites will then, in turn, be converted into the much less harmful compound Nitrate by bacteria known as Nitrobacter and Nitrospira. We can then remove these nitrates via water changes and, essentially, dilute them with clean water.

But what happens when we hit a sticking point? What happens when our aquarium cycle, effectively, stalls? We keep testing but we keep seeing high levels of nitrite in the water. Our ammonia levels are fine, we can see nitrates in our test results, but the nitrite levels just won’t go down. Even after weeks and weeks?

Why Do Nitrite Levels Stay High After Cycling?

This is, probably, the most common scenario that will keep people cycling their aquarium for months on end. Nitrite levels can be very stubborn due to how much they accumulate while we are waiting for the bacteria that can convert them to nitrates to grow and split.

The fact of the matter is, nitrite is the second part of the nitrogen cycle so is consistently accumulating. If our ammonia levels are dropping, nitrite will levels will be increasing as the ammonia is converted into nitrites. For a decent length of your aquarium’s cycle, there won’t be any bacteria there to convert the nitrites into nitrates.

The reason for this is that we need nitrites present in the water before the bacteria that converts nitrite into nitrate will appear. Giving the nitrites an uninhibited period of time to accumulate. This issue is compounded by the fact that the bacteria that converts nitrite into nitrate, Nitrobacter and Nitrospira. Takes far longer to split off and double than the bacteria, Nitrosomonas, that converts ammonia into nitrite.

In ideal conditions, Nitrosomonas bacteria will take 6-10 hours to double. We struggle to provide these ideal conditions in the aquarium so it is far closer to 16-24 hours. Nitrobacter and Nitrospira can be double that length of time. When there is a decent accumulation of nitrites in the water, it can take even longer as the presence of high levels of nitrite will slow the growth rate of Nitrobacter and Nitrospira bacteria.

The whole time that the ammonia converting bacteria, Nitrosomonas, has been doing its job. Nitrite levels have been building and that ammonia converting bacteria had a big, big, head start. Now our Nitrobacter and Nitrospira bacteria is growing and reproducing at a slower rate, due to the high levels of nitrite, and it has a big backlog of nitrites to get through. This can take months and months.

The Reality of Nitrite in a Saltwater Aquarium

So now you should be able to see why nitrite levels are so stubborn in a marine aquarium. There is a big backlog of them to get through and the bacteria that converts nitrites into nitrates grows and reproduces at a much slower rate. But there is something that is quite important about nitrites in a saltwater aquarium that we should elaborate on.

The truth of the matter is that nitrites, in saltwater aquariums, are less of an issue than they are in freshwater. At standard levels, they really shouldn’t cause harm to your aquarium’s residents. We are going to explain why in just a second.

I know! It sounds absolutely ludicrous. Especially when you take into account the opinions of hobbyists who are pretty vocal about the opposite opinion. Or those who came from freshwater aquariums and have rigid view points derived from that hobby.

Whereas nitrites in freshwater are lethal, preventing the carrying of oxygen around a fish’s body. Effectively suffocating them as the nitrites bind to the fish’s Haemoglobin. Converting it into something known as Methemoglobin which doesn’t carry oxygen in the same way Haemoglobin does.

In salt water, the high levels of the compound chloride in the salt will outcompete the nitrite. Both chloride and nitrite are negatively charged ions that compete for the same sites on a fish’s gills. The abundance of chloride in saltwater means that there isn’t much of a battle. With the chloride preventing the nitrite from being absorbed into the fish’s body by taking up all the space. Making nitrite, at typical cycling aquarium levels, less of a concern in marine fishkeeping.

Should We Worry About Nitrite in a Salt Water Aquarium?

The simple answer here would be “Yes, we probably should still worry” but there is a “but” in there, somewhere. We should worry about the nitrite levels in our saltwater aquariums because they may indicate a problem with our nitrogen cycle. Your nitrite levels being off might suggest a problem with the levels of bacteria in your aquarium, for example.

The “but” comes from the fact that the presence of nitrites shouldn’t be particularly harmful to our aquarium’s residents. Those that carry oxygen via Haemoglobin should be fine, at the very least. There is, however, limited evidence as to how things like coral will be impacted.

In fact, many experienced marine aquarium owners don’t test for nitrites at all. Seeing it as a waste of time as nitrite levels would never come remotely close to what would be considered harmful in a marine aquarium. This is particularly true when you are first cycling a marine aquarium as nitrite levels are bound to be fairly high. Therefore, not necessarily indicative of a problem; they are more the result of the process that is taking place in our tanks.

Can I Consider My Cycle Complete While Having Detectable Nitrites?

I don’t think that you can, strictly speaking, consider your cycle complete while you still have detectable levels of nitrite that won’t drop. But I don’t think that this is indicative of a problem or indicative of your aquarium’s cycle having stalled.

Further to that point, I think you can go ahead and add clean up crew to your aquarium while you have detectable nitrites. The main factor we are looking for is the ammonia levels dropping to 0. When your aquarium can process 2PPM of ammonia to 0PPM in under 24 hours, your aquarium should be safe for saltwater creatures.

I, also, think that you can add a small fish, or two, while you have detectable nitrites. Just be sure to take it very slow for those first few weeks. Consider not adding another fish until your nitrites have actually gone down to 0. If you really want to get those nitrite levels down to 0, however, we can help that process along.

How To Reduce Nitrites in a Newly Cycled Marine Aquarium

It is completely understandable if people want to drop their nitrites to zero before adding residents to their aquarium. After all, people who believe in reducing nitrite levels to 0 only have the best interests of their fish at heart. The process is fairly simple and quite similar to how we deal with high levels of ammonia in a cycling aquarium. Let’s create a plan of action.

• Verify that your nitrite test kit is accurate
• Perform a large water change of 25-50%
• Give your bacteria a boost with some bottled nitrifying bacteria
• Carry on adding ammonia daily until your nitrite levels begin to drop

The first suggestion, in this list, is rather simple. Verify that your nitrite test is accurate. You can do this by testing some deionised water or by mixing up some fresh saltwater and testing that. The test should, obviously, come back negative for nitrites. If it does, your test should be accurate.

Give Your Bacteria a Helping Hand

We now want to perform a large water change. As large as you can possibly manage. This is going to drop our nitrite levels immediately and give our bacteria a bit of a helping hand. Don’t worry! You won’t be removing bacteria from the water by changing it. It’s a common misconception that bacteria lives in the water. It doesn’t! It lives on the surfaces of your aquarium like the rocks and sand.

We then want to give our bacteria a big boost by adding a bottle of nitrifying bacteria. This bottle will contain everything we need including Nitrosomonas bacteria for ammonia and Nitrobacter and Nitrospira bacteria for nitrites. This will help your aquarium’s cycle along significantly. Keep dosing the bacteria each day, as per the instructions, and your nitrite levels should begin to fall.

While this is going on, we want to be continuing our cycle as normal. After all, those ammonia converting Nitrosomonas bacteria still need to be fed. Keep adding ammonia or ghost feeding while this is going on and keep measuring both ammonia levels and nitrite levels. When nitrites drop to 0, you can truly say your cycle is complete.

In Short

To quickly summarise this article on high nitrites while cycling your marine aquarium. Nitrites are a by-product of the nitrogen cycle that can accumulate due to the slow rate at which the bacteria that converts nitrites into nitrate, Nitrobacter and Nitrosira, grow and reproduce. While nitrites are less of a concern in a marine aquarium due to the interaction between chloride in the salt and nitrites in the water. We can reduce them with water changes and by adding bottle nitrifying bacteria. Thank you very much for reading and for spending time with me here on Simple Reefs.