I just thought I would take some time to explain some of the methods that can be used to cycle a marine aquarium in a little more detail that what we currently have on our forum. The nitrogen cycle in a marine environment is similar to that of the nitrogen cycle in a fresh water environment. In both environments you have nitrifying bacteria that coverts ammonia into nitrites and nitrites into nitrates. While the nitrifying bacteria in a marine aquarium are different bacteria then the nitrifying bacteria in a fresh water tank, they do perform the same functions and essentially work the same. A marine nitrogen cycle has the addition of de nitrifying bacteria which converts nitrates into nitrogen gas. I will be making many comparisons between the fresh water and salt water cycling methods through this article in order to better illustrate some points better for people who are new to salt water aquariums.
I do not suggest cycling a marine tank with fish for two reasons. The first reason is that there a very few marine fish that can tolerate lower levels of ammonia in the water. The second reason is the larger water changes required to keep the safe for even the hardiest of fish would make it very difficult to maintain your PH stable enough for any marine fish not to mention the extra cost of the salt.
The first step is to decide what type of biological filter media you are going to use. Regardless of what type of biological filter media you choose, you will need to cycle your tank before adding any type of stock to the tank. The two most common methods used are: biological filter media just as you would use in a fresh water filter, and rock (both live and dry) from the ocean. Each has their good and bad points. For any cycling method you want to use a good quality salt. While cycling (regardless of the exact method), you will need to maintain your salinity between 1.025 and 1.027 and your temperature between 78F and 82F. You won’t have to worry about testing for alkalinity, calcium, or magnesium until after the first part of your cycle is finished.
Cycling with Biological Filter Media
This process is very similar to the freshwater fishless cycling process we have on our forum which is described in the below link:
This process is best suited for when you want to use a biological filter media in a typical hang-on-back filter (HOB) or a canister filter just as you would expect to use on a fresh water tank.
You will need to add a source of ammonia to start growing your beneficial bacteria (BB). You can get this from: adding a piece of raw shrimp, adding fish food, or by adding pure ammonia. It is best to use pure ammonia so you can have better control over the process. When using pure ammonia, start the process by bringing your ammonia up to around 2ppm. A little higher is OK as well. As every manufacture makes there pure ammonia at slightly different concentrations, there is no set amount per gallon to add. It is always best just to add a very small amount, wait an hour or so, test your water, repeat as required. Once you have worked through that initial dosing, you will now have an accurate measurement of how much ammonia to add to bring your level up to 2 ppm. Check your ammonia levels daily. Once you start to see your ammonia drop, dose once each day to bring it back up to around 2 ppm. At this point you start testing daily for nitrites as well.
When your nitrite level spikes around or over 2ppm, start maintaining your ammonia level around 1ppm. Only dose ammonia once each day to bring it back up to 1 ppm. At times your ammonia will fall to 0ppm and that is OK provided that you bring it back up to 1ppm only once each 24 hour period. When you start to see you nitrites falling, start testing for nitrates as well. When your ammonia and nitrites are both 0ppm within 24 hours after dosing your ammonia back up to 1 ppm, and your nitrates are rising, you have completed the first part of a typical cycle and now have successfully grown the nitrifying bacteria you need. You can now slowly start stocking your tank. If it will be a while before you will be adding any fish to the tank, you will need to add a drop or two of ammonia to the tank to keep the bacteria feed and alive.
The benefits of this approach are that it is easy to do and it is the lowest cost method to cycle a tank. The drawbacks of using this method is that your filter media will require frequent cleanings to avoid any build up of crud in the filter media which is extra work and will limit any growth of the denitrifying bacteria. Using a filter can also be problematic for reef tanks making this approach more suited for fish only set-ups.
Cycling with Dry Rock
You should first cure your dry rock by soaking it in dechlorinated fresh water until all the nitrates and phosphates have been leached out. The below link explains that process
Cycling with dry rock is basically the same as cycling biological filter media. Your dry rock is the biological filter media in this case. As a general rule of thumb, you will need ~1 lb of rock for each gallon of water. Follow the exact same process as described for cycling with biological filter media. Once you have completed the first part of your cycle and added your fish, keep checking your nitrate levels. Within a few weeks you will notice a drop in the nitrate levels as the denitrifying bacteria grows. I have personally used this approach and it works well.
The benefits of this approach is that over time, the denitrifying bacteria will grow on your rocks and help you control your nitrates. There also is very little maintenance involved with using rock in your tank. You can also use this approach for reef and fish only set-ups. The drawbacks can include the extra cost as compared to using a filter and a little extra time curing your dry rock before adding it to the tank.
Cycling with Live Rock
This is my preferred approach to cycling a tank. When compared with cycling a fresh water tank, cycling with live rock is like adding both a source of ammonia and using already seeded/cycled filter media. When cycling with live rock, you should still use the general rule of thumb of having ~1 lb of rock for each gallon of water in your tank. The information on curing live rock (link below) explains the rest of the process.
When it comes to live rock, the process of curing the rock is the same as cycling the rock. The only difference here is that you do not want to add any ammonia while the tank is cycling. You still have to check your ammonia levels daily to make sure your ammonia will not get above 2ppm, and completing a water change if it does. You also have some options to keep your costs down. You can use partial amounts of live rock and dry rock to cycle your tank provided you use a minimum of 20% live rock. Once the first part of the cycle is complete, you’re ready to add fish. If the tank is going to sit empty for a while after the first stage of the cycle is complete, you should add a drop or two of ammonia every day to keep the bacteria fed and alive, but it should be OK for a least a few weeks / months before you would have to worry about doing that.
Note: it is always best to cure your live rock outside of your set-up. A quarantine tank without any lights would work best. This will help you latter to control your nitrates as well as help you avoid introducing something bad into your set-up
The benefits of this approach are the shortest time to cycle a tank as well as the shortest time to grow your denitrifying bacteria. Sometimes the first part of the cycle can be as short as s few days. You can also use this approach for fish only or reef tanks and is the best suited one for a reef tank. The only potential drawback is that live rock can be the most expensive approach to obtain biological filter media.
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