In this post I’ll tell you how to lower high nitrates in your saltwater aquarium with table sugar.

What are Nitrates in a saltwater aquarium?

Nitrates are the waste by-product of nitrifying bacteria (Nitrobacter), which develops in the final phase of the nitrogen cycling process. It is what makes an aquarium’s biological filtration system function and stay in balance.

Uneaten fish food and fish waste start the nitrogen cycle as ammonia. Ammonia breaks down into nitrites and nitrites break down into nitrates.

Nitrates should be as close to 0 as possible in your saltwater tank. Although nitrates at higher values will not harm fish, high nitrate levels will kill your corals.

How to remove Nitrates from a saltwater aquarium

Removing nitrates from a saltwater aquarium is more about prevention than it is maintenance actually. Here are some ways to remove nitrates from your saltwater aquarium.

• Do weekly water changes of at least 10%. Remove 10% of the saltwater in your saltwater tank by vacuuming the surface of your sandbed and then replacing the 10% of saltwater removed with new saltwater you either make at home or buy at the local reef store.
• During your 10% weekly water change, blow off the rocks (rockscape) with a turkey baster. This will remove all uneaten fish food and fish waste from the rocks so they can be picked up by your saltwater aquarium’s filtration system.
• Do not overfeed your fish. I know you want to feed the poor fish as much as they can eat, but overfeeding will only result in excess food rotting, which adds to your nitrate problem in your saltwater aquarium.
• Do not used crushed coral for sand in your saltwater aquarium. Crushed coral has spaces where fish waste and uneaten fish food can get stuck and rot.
• Do not overstock (too many saltwater fish) in your saltwater tank. The more fish you have, the more fish waste you will have, which will contribute to your high nitrate issue.
• Change your filter media often, at least every 3 days to a week (if you have smaller fish.) Filter media catches all uneaten fish food and fish waste. You don’t want your saltwater being filtered through soiled filter media.
• Clean your protein skimmer and vacuum out your saltwater tank’s sump every 6 months to keep it free of debris, uneaten food and fish waste. Some saltwater aquarium hobbyists do this deep cleaning every few months, while some do it once a year.

After doing maintenance on your saltwater aquarium to lower nitrates and you find you are still having a high nitrate problem, you can try carbon dosing.

Carbon dosing is when you add carbon to your saltwater aquarium in the form of table sugar or alcohol (yes that alcohol.) I will be speaking on table sugar since it is cheaper and easier to dose to a saltwater aquarium.

Adding sugar to your saltwater aquarium (known as carbon dosing), feeds the Anaerobic Bacteria in your saltwater aquarium. This Anaerobic Bacteria lowers nitrates in your saltwater aquarium by feeding on the nitrates.

When the population of Anaerobic Bacteria grows in your saltwater tank, by feeding it table sugar, the oxygen level will lower a bit in your saltwater tank.

In order for this method of lowering nitrates to work in your saltwater tank, you must have a protein skimmer running. The protein skimmer will export the nitrates and dying Anaerobic Bacteria, while also oxygenating your saltwater.

Carbon dosing is feeding Anaerobic Bacteria sugar, which increases the population of Anaerobic Bacteria.

Anaerobic Bacteria removes nitrates via sugar dosing in a reef aquarium. As you add sugar daily, Anaerobic Bacteria will populate and lower nitrates dramatically.

You must have a protein skimmer for this procedure, which will remove the excess bacteria, taking the nitrates with them.

The amount of sugar dosed is very small. Your Saltwater tank more than likely will get cloudy and that is ok. If your saltwater tank gets cloudy, either cut the dose of sugar in half or dose every other day.

A cloudy saltwater tank simply means you dosed too much sugar and the Anaerobic Bacteria population is blooming very fast. The cloudy water will go away within a day.

The amount of table sugar I add (you can add sugar to the sump or the tank directly) is 1 teaspoon sugar per 60 gallons per day.

Once your nitrate level reaches 0 (takes about 2 weeks or less), you can continue dosing sugar once or twice a week to maintain low nitrate levels.

Some saltwater aquarium hobbyists see carbon dosing as a bandaid fix, while others say it’s a tool to control nitrates. These same people who say carbon dosing is a bandaid fix are usually known to dose all kinds of chemicals to their saltwater aquarium. I stay away from chemicals and let Mother Nature handle things.

You should find the source of your high nitrates in your saltwater tank and why they are spiking and correct it at the source.

I suggest you use sugar dosing to keep nitrates to a very low level after you have exhausted all other means: do not overstock your tank, clean mechanical filtration and perform water changes.

I perform a weekly 10% water change on my saltwater tank, have removed my foam block from the tank, and always run a protein skimmer. My nitrates have jumped to 20 ever since I added a new larger fish to the tank. That could be it. I also vacuum the sand bed thoroughly.

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