Why do we need so much filtration in a saltwater tank?
Animals that have lived in the ocean need to have a very stable environment. They have evolved in an environment that has basically stayed the same for the last few million years. It is a lot different than living on the surface. There's no temperature spikes, weather spikes or anything else that affects us here on the surface for the most part. When you keep these animals in a reef tank environment, extra special care needs to be made for the chemical balance of the water. Specifically the nitrogen cycle. The nitrogen cycle is how waste from the animals in the reef tank decompose into less toxic chemicals. The more water volume you have, the easier this becomes. The same amount of toxic chemicals do less damage in a larger volume of water. There are many ways to filter the water in your reef tank, and this article will outline some of my favorite filtration methods.
Live rock is one of the most important and popular filtration methods for any kind of saltwater tank. It requires almost no maintenance, last forever and is aesthetically pleasing once it is cured. Live rock has a twofold filtration purpose. The first one is that it adds more surface area inside your tank for beneficial bacteria, and all the little holes and crevices are home to another special kind of bacteria that lives in only oxygen devoid areas. This means that live rock completes two out of three steps of the filtration in your reef tank. Live rock is very expensive if bought in your local fish store, averaging about $12 a pound. The recommended amount of live rock that should be used for filtration is 2 pounds per gallon of water volume. I had 400 pounds in my 200 gallon tank.
Deep sand bed (DSB)
The deep sand bed (DSB) method of filtration seems to be one of the most controversial methods. But I think most of the controversy stems from a static application as opposed to good science. The scientific findings behind this. Filtration method are rock solid, it works. The general concept is to have a deep sand bed, made of a calcium-based sand, with fine sized grains, likes sugar. There are lots of bacteria in your reef tank. The basic function of a deep sand bed is to promote the growth of the bacteria that lives in the oxygen depleted zones of the bottom layers of the deep sand bed. These kind of bacteria get their nutrients from nitrogen, as opposed to oxygen. This is perfect because fish and coral waste is mostly ammonia, this decomposes into nitrites. The bacteria that live on the surfaces present in your reef tank feed off of these nitrites. By having a sand bed in your reef tank, instead of a flat glass surface, you increase your surface area almost threefold, which in turn increases your filtration ability for this stage of the nitrogen cycle threefold. these bacteria use the nitrates which decompose it into nitrates. the next kind of important bacteria that we have in our reef tank live in the anaerobic or the oxygen depleted zones of our reef tank. the biggest oxygen depleted zone is the bottom layers of the deep sand bed.
Protein skimmers are fairly simple devices. In fact, skimming is used on a large scale in the oceans naturally. Do you ever notice the foam that collects on a beach? Well that is protein based fish waste. These proteins stick to water-air surfaces. When a wave breaks, it causes millions of bubbles of various sizes to form and rise to the surface with the waste attached, hence the foam. A protein skimmer is a cylinder tube with water pumping through it. Attached to the pump is a venturi where air is sucked into the water stream, hitting the propeller of the pump and turning into tens of thousands of tiny bubbles. All of these bubbles have a air-water surface and collect protein waste that touches it. These tiny bubble then rise to the top of the skimmer and end up over flowing into a cup attached to the top of the skimmer. You are then able to remove the cup and dump the waste easily. This removes the waste without binding chemicals and doesn't remove needed minerals from the water column.
A sump is basically a second tank, usually below your display tank in the stand, where most of the filtration and maintenance equipment is kept. The water circulates from the display to the sump in a overflow, then back to the display tank via pump. Having a sump is a necessity for a reef tank in my book. Everything you have done so far with live rock, deep sand beds and water volume can be doubled in a sump. If you don't like the look of the deep sand bed, you can keep it in the sump out of sight. I recommend you put a second deep sand bed in the sump and double your nitrate reduction capacity. This is the method I always use and it creates great filtration and chemical stability. With two deep sand beds you won't have to worry much about supplementing calcium till your coral load gets fairly high as well.
Do you know what plants need to grow? Nitrates. We can use this to our advantage when setting up a reef tank. We simply make a place in the sump for macroalgae such as Cheato and red mangroves. These plants take up the No3 (Nitrate) in the water column, which is the third and final step of the nitrogen cycle in your reef tank. These plants require a light misting of fresh water from a spray bottle for the mangroves, and a pruning of the Cheato about every other month. I just rip it in half and throw half of it in the trash.
I hope you liked my article and please check out some of my other reef articles here: