Let’s take a quick look at the ocean – it is a vast area which is exceptionally dynamic. The animals which live in the ocean, some of which make it to our aquariums are used to the action of the water movement.
The secret of a successful marine aquarium other than research and patience is optimum water quality, adequate lighting and water movement.
Water movement is not something which is appreciated by marine aquarists but is normally something which is provided as it is believed that it needs to be provided. To appreciate the important of water movement it is important to understand its role in nature, understand the requirements of the animals and then finally work out the best way to provide the required water movement.
Water movement’s role in nature is for many things. It allows for gas exchange, the provision of dissolved oxygen, the provision of food to animals, the removal of waste, the exchange of nutrients between filtration methods (In the wild this could be between the reef itself and grass beds/mangroves etc).
Water movement within the home aquarium has a simple term which is simply ‘turnover’ which is also classified as the amount of water which is moved around the aquarium per hour. There is a standard minimum turnover for a reef aquarium which is 10 times per hour. Therefore if you have an aquarium which is 100 gallons then you will need to ‘turnover’ the aquarium water 1000gph.
It is not as simple as purchasing the correct amount of water pumps, powerheads, wavemakers to facilitate the correct amount of turnover. There will be some fine tuning required in order to provide the correct types of currents to the animals in the aquarium. This is especially true when corals are being kept as their water movement requirements are higher than that of fish. Corals unlike fish do not have the ability to be able to walk around the aquarium in search of the ultimate spot. Some anemones do have this ability and move around the aquarium looking for the perfect location. Unfortunately quite often this is round the rear of the tank out of sight!
I shall have to get a little bit scientific here in order to explain why corals require strong water currents. Hopefully it will not get confusing. When water flows around a coral its viscosity increases due to friction. At the water/coral interface the water is at its highest viscosity – basically the water becomes really thick and due to this a stagnant area of water is evident around the coral. When this happens the coral literally poisons itself due to the inability for diffusion to occur. Obviously this is not something that we want to happen and the correct amount and type of water movement needs to be implemented. We cannot just point an outlet from a powerhead directly at a coral as this will not be appreciated and could again kill the coral.
Whilst fish do not have the same requirement for strong water movement as corals do there are a lot of fish who respond better when kept in an aquarium with strong water currents. Feeding time is more natural and the fish continuously move themselves around to be in the correct flow pattern where both essential oxygen and food is provided.
Another area to consider is the filtration itself. If live rock is used then enough water movement needs to be provided to allow the water to be able to move over, around and into the rockwork so that the bacteria can do its job. If not enough water movement is provided there will be areas in the aquarium where the water is not moving and stagnant. These areas effectively become bad and are not being processed by the filtration. Live rock can only process the water which passes over it therefore if the water is not moved to the filtration area then quite simply it will not get processed and before long the water quality will begin to suffer. From here the slippery slope begins.
One area which is often forgotten about is the air interface – the surface of the water. If flow water movement is provided then the low oxygen areas in the water will stay near the bottom of the aquarium and the oxygen rich areas near the top will stay near the top. For the air/water exchange to work effectively the surface of the water needs to be broken. This can be achieved in many ways – it can be achieved using a spray bar, a small powerhead pointing up to the surface of the water or can with enough water movement in the aquarium be created all on it’s own.
What we need to achieve is a lot of water movement in the aquarium using what is called a wide flow. The output from a powerhead is a thin flow and whilst powerful is damaging. The flow itself does not want to be laminar in pattern i.e. all in one direction instead it needs to be chaotic/turbulent.
Looking at the corals in the wild we can see that they sway in all directions as the water currents move them around. If you have ever been scuba diving or even snorkelling on/over a reef then you will appreciate how water movement in nature works.
Another type of flow which is very popular is what is called surge flow where the water flow in a back and forward type of action. There are various devices available which assist in the creation of this type of flow and also various do it yourself plans available however personally I believe that even this type of flow needs to be broken up so that is becomes turbulent.
I am a firm believer in trying to emulate nature as much as possible in the home aquarium and water movement is no exception. Quite often in the wild the water currents reduce due to the lack of wind at the waters surface. Again this is relatively easy to achieve with a light sensor which either reduces the speed of the pump or turns it off altogether.
The aquascaping in the aquarium will also have an impact on the flow in the aquarium. When the water flow hits or passes over the rocks then friction will occur and this will effectively reduce the amount of flow in the aquarium. The same can be said for corals especially hard corals as they grow larger. As they grow the flow in the aquarium will change and will need to be periodically reviewed. Due to the rocks and corals in the aquarium there will be areas of the aquarium where the water flow is significantly different. This is not too much of a problem as long as corals are placed in locations which are suitable for their requirements – both water movement and lighting. It is imperative however to ensure that there are no areas of stagnant water as this will create problems further down the road.
When planning the water movement in the aquarium there are normally two factors which are taken into consideration. The first one is the requirements of the animals in the aquarium and the second one is cost.
Powerheads are normally the aquarists first choice as they are cheap to purchase and can create good flow within the aquarium with careful positioning. As already stated we need to be careful to ensure that the flow is not pointed directly at a coral as damage can occur.
Wider pumps are available which have a much wider outlet and instead of an impellor have a propeller type device and this creates a strong yet soft flow if that makes sense which therefore means that flow can be provided which is much more beneficial to the corals in the aquarium. Care still needs to be taken with placement so that no damage is caused to the corals however the flow created is much more natural.
There are various other methods which can be utilised. Wavemaker devices can be implemented to create random flow. These can be automated devices which switch pumps on and off to create a random flow. Again care does need to be taken with these are powerheads/pumps are not created to be turned on and off all the time and damage can occur to the powerheads/pumps. Other wavemaker devices are also obtainable which are similar in design to those of wavemaker devices in swimming pools.
Another option which is my personal favourite is the implementation of what is called closed loop. This is where the pumps are located outside of the aquarium and flow is directed into the relevant areas of the aquarium using pipework.
It is my opinion that water movement is one of the six important factors of a successful home aquarium.
Planning, patience, research, water quality, lighting and water movement.