The flow is one of the most important factors in running a saltwater aquarium. Particularly corals depend on sufficient water movement to transport food, dissolved substances and gases to and from the animal. The boundary layer, in which an unfavourable micromilieu for the coral can develop, should be reduced to a minimum. Only in this way processes such as photosynthesis and calcification can function without problems.
When planning a reef tank, special attention should therefore be paid to the flow (and not only to the lighting).
Below are a few tips for an optimal flow pattern:
️#1 Multiple stream pumps are better than one
And this already applies to smaller nano tanks. With several stream pumps, the deposition of detritus can be avoided and an even flow around the reef structure can be achieved.
#2 Use oversized and controllable pumps
Due to the growth of corals, the flow may have to be adjusted after a while and may even have to be increased. It is therefore best to use controllable pumps that initially run at reduced power. As a rule of thumb, the MINIMUM power of the selected pump should be about 10 times the volume of the tank per hour; for a tank stocked exclusively with SPS corals, it is better to use 30 to 50 times that.
Flow-loving corals: Encrusting growing Montipora, thick-branched Acropora and Stylophora belong to the ultimate flow lovers among stony corals. The formation of a solid calcareous skeleton (like here in the picture: Stylophora pistillata) is an adaptation to withstand strong currents. In nature, these corals are often found in the area of the reef crest.
#3 Flow-friendly reef design
Even the strongest flow pump is useless if it hits directly against a reef wall. Use reef decoration, like live rocks or ceramics, therefore sparingly and use large elements lengthwise to the flow. Avoid flow shadows and also pay attention to unnecessary loss of performance when decorating technical elements (e.g. stream pumps).
#4 Positioning of the pumps
As long as it does not disturb optically, the stream pumps should be positioned diagonally to each other, so that a kind of ring flow is created in your tank. For larger and especially elongated reef aquariums, several pumps can be distributed along the length. In the upper (more strongly lit) area of the aquarium you should create more current than in the lower area. However, the current must also be strong enough to prevent the formation of "dirty corners". Make sure that the flow does not create too many waves on the surface, otherwise there is an increased reflection and less light reaches the corals.
#5 Flow according to the stocking
Particularly with a flow-loving stock such as SPS corals, gorgonians, soft corals and tangs, a strong flow pattern should be maintained. LPS corals, zoanthids, anemones and dragonets, on the other hand, belong more to the " flow mouffles ".
#6 Aim for a laminar flow
Laminar flow patterns come closest to natural conditions, but are difficult to realize in an aquarium. Constructions with perforated plates can be a solution here. In any case, pump outputs should not be directed directly towards each other to avoid turbulence.
There are exceptions to the rule: While most corals prefer laminar flow patterns, Zoanthids like it turbulent. A good placement for Zoanthids in a reef aquarium are therefore areas where the flow is breaking up.
#7 Controllable stream pumps
With the help of controllable stream pumps, flow strengths can be varied during the day, waves or tides can be simulated and flow directions can be changed. The latter is ideal for further reducing areas with low flow.