How Do You Know When Your Saltwater Tank Is Cycled?

The most commonly asked question I get is this. How do you know when your saltwater tank is cycled?

One of the most important things you need to have if you want success in the saltwater aquarium hobby is patience.

I know when setting up a new tank, you want it to be ready for livestock right away but that’s just not how things work with saltwater tanks. The tank is going to need time to mature and cycle first before adding any fish or corals.

It can be frustrating and really test your patience as sometimes it seems like cycling a new tank can take forever.

How do you know when your saltwater tank is cycled?

You will know your saltwater tank is cycled when the Ammonia and Nitrite levels reach 0. This will take approximately 4-8 weeks. This is where patience comes in.

Make sure that you use a reliable test kit to check your levels. Many hobby grade test kits are just not accurate and reliable enough to be trusted.

How to cycle a saltwater tank

To begin the cycling process we need to look at the Nitrogen cycle.

This is where the beneficial bacteria begin to build up in your aquarium, breaking down harmful ammonia(NH3) into nitrite(NO2) and then nitrate(NO3). As mentioned, this can take anywhere from 4-8 weeks.



It’s a good idea to start your cycle with live rock. If that’s not available to you, the dry rock can be used. Using live rock has its benefits like reducing the cycle time and adding beneficial bacteria to your system, but you also risk the chance of introducing hitchhikers into your tank.

If you can get your hands on a healthy large piece of rock that has been established in a saltwater tank for a few months, it would greatly help your tank cycle. Any form of beneficial bacteria like filter media, bio rings, etc.. is a bonus.

Pro tip: Do not use fish to cycle your tank! You will hear many people say that you can just use a tough fish and plop it in the tank right away and use it as an ammonia source, but that is just not the right thing to do.

Fish can add an ammonia source that is too much for your tank at first, cause levels to spike, and can be a disaster. Not to mention it is very stressful and harmful to the fish.
After adding an ammonia source like rotting fish food, wait a week or so and slowly add some invertebrates.

Over the next few weeks check your water levels on a consistent basis and keep an eye on your ammonia and nitrite levels. Once they reach 0, your tank is fully cycled!

How long should a saltwater tank cycle before adding fish?

It’s important to let your tank fully cycle before adding new fish to the tank. This can take anywhere from 4-8 weeks.

Do you do water changes when cycling a tank?

It is beneficial to perform small water changes during the cycle period. It helps dilute ammonia and nitrite which is a good thing.

Some people will say that performing a water change during the cycle period will slow down the process, but I believe that is not true. Reducing the amount of ammonia or nitrites won’t slow the cycle down.

Also removing water during a water change will not remove the beneficial bacteria. Most of the bacteria will be on the rocks, sand, and gravel, so don’t worry about removing water. It won’t have a negative effect.

How to cycle a saltwater tank faster?

saltwater live rock

If you are so impatient and don’t want to wait the 4-8 weeks for cycling, there are a few things you can do to speed up the process. It may still take a while but adding some mature beneficial bacteria is the key to helping a tank cycle faster.

I mentioned earlier about using live rock. This is the best way to reduce cycle time. Perhaps you know someone with a healthy established saltwater tank and you can grab some live rock from them. Most saltwater fish stores also sell it, you won’t need much depending on your tank size.

You can also use well-established filter media, live sand, ceramic bio rings and place it in a hang-on filter or sump. Another option you can use is a nitrifying bacteria booster or starter. You can buy this online or at your local fish store and it will help seed the tank and speed up the cycle time.

Marine Depot Aquarium Supplies

How to cycle a saltwater tank with dry rock?

Starting a saltwater tank from scratch with dry rock is the only way to ensure you don’t introduce hitchhikers or anything bad into your tank.

Dry rock is considerably less expensive than dry rock as well and is easier to get. One of my favorite types of dry rock is the Natures Ocean coral base rocks. They are very affordable and look great in your tank.

The downside of using dry rock is that it really doesn’t provide any benefit to help cycle your tank. There is no beneficial bacteria on it so it won’t help the cycle. But it also won’t hurt it. A general rule of thumb with dry rock is to use 1 pound of rock for every gallon of water you have.

This will depend on your tank size and dimensions, but for example, if you have a 75-gallon tank, you can use anywhere from 60-80 pounds of dry rock.