Biology and Biofiltration in Reef Aquariums

Introduction: The Connection Between Biology and Chemistry

The first thing you should understand about creating a beautiful reef aquarium is that biology is directly related to chemistry. In other words, chemistry in a marine aquarium won't matter without biology: all chemistry affects biology, and biology can also affect chemistry.

It's important to understand that chemical elements exist in biologically active forms. This means there is biochemistry and there is just chemistry. For example, there is organic calcium and inorganic calcium. As you likely know, only biological (organic) calcium is well and easily absorbed by corals and other marine organisms.

Active and Inactive Forms of Elements

The Iodine Example

There is elementary iodine (brown with a distinct smell) and forms of iodate and iodide, which are basically not absorbed until they turn into the elementary form. It's the elementary form of brown iodine that gives effects in coral staining – the tips of corals become blue.

Manufacturers often sell iodate or iodide – a clear liquid with no color difference from ordinary water. When you dose this form of iodine into the aquarium, biological processes partially turn it into an active form (elementary iodine), and only then do you get those effects, not immediately.

If you dose brown iodine, you must not overdose it. This iodine immediately enters all biological processes and can have both positive and negative effects if overdosed.

The Tin Example

There is inorganic tin which is essentially non-toxic, but organic tin is a toxic form that adversely affects all bio-organisms. If overdosed, your corals will simply die.

You can do an ICP test and see that the amount of tin in your aquarium is about 100, and there will be no problem. But if this tin is in organic form (which ICP won't show), then you can have a problem. Even when tin rises only 5 milligrams per liter, this is already a big problem.

Phosphates and Magnesium: An Important Relationship

If there is an overabundance of phosphate in your marine system (higher than 0.3 mg/L), the calcification process is disrupted. Phosphate molecules take the place of magnesium molecules, and coral skeletons start building up much slower or cease to be built at all.

The calcification process in the marine system is disrupted, and with large amounts of phosphate, you may notice that live rocks start to crumble in the aquarium. You'll see a lot of sand constantly pouring out of stones. This is exactly the process of destruction influenced by a large amount of phosphate when calcium structures begin to collapse and corals naturally stop growing and gradually die.

The Nitrogen Cycle and Carbonate Hardness

What is the Nitrogen Cycle

The nitrogen cycle is the transition of ammonia, which is released by fish, the remains of rotting feed, and everything that can rot in the aquarium. Ammonia turns into nitrite and then into nitrate. This whole process is called the nitrogen cycle.

Impact on Carbonate Hardness

A certain amount of carbonate hardness is used for the nitrogen cycle process. If you, for example, feed fish too much, a lot of ammonia is produced in your system. As a result, a very powerful nitrogen cycle is launched, which also consumes a large amount of carbonate hardness.

If you overfeed, usually after two or three days, the level of carbonate hardness decreases. But you should understand that the carbonate hardness hasn't gone anywhere – it's just temporarily used and not detected by tests. As soon as the nitrogen cycle slows down again, you'll see a return of carbonate hardness.

Biological Filtration: Two Key Processes

Biological filtration in a marine aquarium consists of two processes:

1. The Nitrogen Cycle – the transition from ammonia through nitrite to nitrate
2. Denitrification – the process of assimilation and consumption of nitrate by your aquarium's biology

For denitrification, phosphate must be present in your aquarium. Originally there is no phosphate in the aquarium; it comes only with feed or if you dose it in the form of nutrients. Therefore, you should maintain a constant level of phosphate so that the denitrification process won't stop.

Causes of Biofiltration Failures

Any process, if interrupted (for example, the nitrogen cycle), will lead to the burst of some lower algae or dinoflagellates. The same thing can happen when the denitrification process is interrupted.

Examples of failures:

• You did not feed the fish the day before, and ammonia just ran out
• Phosphate has fallen to zero in the aquarium
• A fish dies in your aquarium, causing a huge release of ammonia and a very powerful nitrogen cycle

Creating a Proper Biofilter

What is a Biofilter

A real mature biofilter is a live rock. The upper part (about 3 centimeters or 2 inches deep) consists of an aerobic zone where aerobic bacteria that need oxygen have settled. The inner part (black area) is anaerobic bacteria that do not need oxygen but are more stable.

If, for example, there is not enough food in your aquarium (you did not feed the fish), the aerobic filtration area of this rock degrades first. And the anaerobic one is not affected at all, which is why it is a more stable filter.

Creating a Biofilter Without Live Rocks

In the absence of live rocks, you need to create a biofiltering frame. It is made from an ordinary frame often used for frags. Put bio-cylinders or bio-bricks from good material in there.

Start the whole process, turn on the flow, and make sure it passes right through the biofilter freely. There should be no big obstacles; water should wash the whole biofilter. The biofilter matures for around 4 to 6 months.

Starting the Biofilter

Detritus will help you start the biofilter properly. You can ask friends or a store to get detritus when cleaning their system. Turn off the return pump and pour all this detritus right on the frame, allowing it to fall inside and settle well.

In about half an hour, turn on the return pump again. Part of the detritus will splash on your display, but it's not a problem; just remove filter bags if you had put them in and turn off the fleece filter to allow the detritus to settle for a while.

This detritus will provide the initial launch of your biological processes because it contains all the necessary strains of bacteria needed for live systems.

Maintaining Biofiltration

Feeding the Biofilter

You must constantly feed the biofilter, just like you feed your fish. If you have interruptions – for example, you left and no one feeds your fish – the amount of nutrients decreases. Fish do produce something, but it's not enough; it's already less than what is usually produced, and accordingly, the biofilter begins to degrade a little.

Creating a Biological Buffer

To maintain and prevent interruptions of the nitrogen cycle and denitrification process, you can create a biological buffer. This is done simply by pouring a layer of fine coral crumbs (not sand) so that detritus can easily get into these crumbs and accumulate in your aquarium.

These coral crumbs will be, firstly, a buffer of carbonate hardness, and secondly, a buffer of biological nutrition. When detritus accumulates, these crumbs will produce some amount of ammonia and phosphate, constantly releasing them into the water in small quantities, thereby supporting the nitrogen cycle and denitrification process we need.

Controlling Biofiltration with ORP

You can also control these processes by ORP:

• A decrease in ORP indicates that your biofilter is not working well enough
• Too high ORP (above 400, around 450) indicates the amount of nutrients is too little
• If the decrease in ORP is accompanied by a decrease in pH, it means that the denitrification process or nitrogen cycle are too powerful and consume too much oxygen from water

The Influence of Temperature and Salinity on Biology

Salinity

Your biology in the aquarium is adapted to a certain salinity. If you changed the salinity by more than two ppm (for example, from 35 to 33 or vice versa), this may cause a little stress to your biological filters. The bacteria begin to work with a little malfunction.

Temperature

Temperature greatly affects the rate of the nitrogen cycle and denitrification. By raising the temperature, bacteria accelerate, and processes go faster. By lowering the temperature, we get a slowdown of all the same processes.

If you feed with the same regularity and amount of food, then at lower temperatures, you get an increase in nutrients, as your bacteria, fish, and corals consume a little less of these nutrients.

Conclusion

To start the biofilter correctly, you can gradually accelerate by increasing the amount of nutrients. We gradually add fish to the aquarium – for example, first 2 fish for 200 liters of water, then 3, then 4.

If your biofilter is accelerated well, you should maintain its operation constantly. You must feed this biofilter all the time. If you added a certain amount of corals, they consume more nutrients. This will happen in about a week or two when they adapt.

Follow all these directions, and there will be no problems with your live aquarium system. The biofilter will always work, your fish will always be healthy, and corals will grow fast and have very bright colors.