In this blog we're talking flow. What is flow? How do you create good flow? What equipment do you need for flow? We'll cover power heads, wave makers and return pumps. Welcome to the frustrating world of reef aquarium flow!
First off, what is flow? When we talk about flow we're talking about the movement of water in the display aquarium. This is often quantified as a number, the amount of litres per hour that water is turned over in the display. Whilst this is a useful metric to describe the capability of a power head or wave maker it isn't the be all and end all when we're talking about the quality of flow in the display. For example, in an SPS dominant display a figure often touted is circa 75x flow. You could meet this figure by getting one big powerhead and cranking it up so that it meets the 75x rate of flow. What this doesn't account for however is the type of flow generated. If you have one big powerhead cranked up to produce 75x then chances are it will produce a focussed and very direct jet of water in your display. When you factor in your sand bed and your rock work this will undoubtedly blow your sand all over the place, create dead spots behind and around the rock work or both. When you add corals into the mix and their needs for flow the one powerhead option really doesn't cut the mustard. So, what can you do about it?
Splitting flow.
Instead of placing one large powerhead in your display what about if you split it down to two powerheads? Two powerheads producing 35/40x flow each will produce a total turnover of 70/80x which meets the metric requirement but now you've also got flexibility in your flow plan. You can position and direct the flow to hit dead spots or to avoid blasting certain areas in order to stop the sand bed blowing everywhere or to preserve certain corals that may require lower levels of flow. Adversely you can direct more flow towards corals which need more in order to thrive.
Flow types and patterns.
In the ol' days of reefing flow was created by using a powerhead or two which were set to a constant flow, mainly because adjustable pumps weren't available. This created a very one directional flow. Reefers would try to randomise the flow with pump nozzles or by directing multiple pumps towards each other in order to create turbulence. As technology has developed and the drive to create pumps with more functionality has resulted in suppliers creating pumps with flow pattern settings. This could be as simple as the pump turning on and off intermittently for short periods of time creating a pulse effect which mimics waves. This was the beginning of 'wave makers'. Over time, functionality has increased to include settings where wave makers increase the power of each 'pulse' over time and then reduce it before repeating. This mimics the surge of waves hitting a reef. Controllers were then developed to link multiple pumps together in order to create a synchronised flow in the display. Overall, when we're trying to master flow in the display tank we're trying to make sure the needs of the inhabitants are met, whether that be corals, fish or invertebrates. Each will require their own intensity of flow. A way to go about this is to shoot for a general turnover figure and then tweek it from there. Observe the corals, fish and inverts to judge if they're getting too much or not enough flow. Too much flow may be indicated by coral polyps not opening up whilst too little flow may be indicated by detritus settling. You can adjust the direction and flow pattern to try and either increase or reduce the flow. Added to this, when corals grow or you add more to the display this will block and change where flow can reach so over time you may find you need to add flow or change it slightly. There's no exact or simple answer here, alot of it is test and adjust as you go. Welcome to the frustrating world of flow!
What equipment do you need for flow?
Powerheads and/or wavemakers. As we talked about in the previous section you can use both. Alot of it comes down to functionality such as whether you want to link the pumps into a smart reef system so you can set them up on your smart device and monitor their performance, link several pumps together under one non-smart controller or even just run single powerheads on their own. The other part of the decision making for what you want to use is aesthetics. A lot of the powerheads and wavemakers are designed to be as minimalist as possible such as the AI Nero powerheads. Other pumps have a different design in order to push as much water in a wide path such as the Maxspect Gyre. Have a look at the powerheads page here on the site to see what options are available.
Return Pumps.
Now let's talk about something that often get's misconstrued as flow and that is 'return flow'. The return pump's sole job is to return water from the sump to the display tank. The rate of this return water should be enough to maintain the temperature of the entire system as the heater is kept in the sump and heats the water before it is the returned to the display where it inevitably cools. This flow is often added to the turnover of the display tank and calculated as the overall flow of the display. Yes, the return pump does contribute to a certain amount of flow in the display however it is unhelpful to group these things together. As already mentioned, the return pump's sole job is to return water from the sump. All you want from the return pump is something that is reliable, quiet and energy efficient. You can browse the return pumps available here on the Rock N Critters site.
That is a quick and brief overview of flow in the marine fish keeping world. This should give you a starting point to begin figuring out how you want to plan your flow in your system. If you get stuck though, come and see us in store where we are running the wavemakers on a number of the displays or drop us an email or Facebook message and we will be more than happy to help find the right pump for you.