One of the most frustrating aspects of aquarium-keeping with marines is creating optimal water movement in the display. Success is often hampered by other common flaws in planning and plumbing, like inadequate drainage (hole numbers and sizes) and the very rockscape of the display, which too often is crippled without a 4” minimum distance from any wall. Water flow issues can literally make or break a tank. Some popular fishes express neurotic behaviors like “pacing” in slow-flow environments: swimming back and forth against the glass relentlessly as if pursuing their own reflection. Some tangs, for example, will cease this behavior with increased water flow. Sessile reef invertebrates depend on accurately applied water flow to bring food to them and to carry waste away. Their very lives will be threatened furthermore in poor flow environments over time and in ways that some aquarists can easily overlook, like encroachment by algae and poor gas exchange
from the increased thickness of the microlayer than runs anoxic near their body. The dynamic snowballs as waste accumulates, mucus accumulates, bacteria proliferate and ultimately become pathogenic; it’s the very thing that kills so many corals in shipping. There is also the simple matter that an increase of water flow in traditionally under-filtered aquariums often translates into prompt and improved rates of growth in captive animals. And finally, on more elemental level, effective water flow is necessary in the aquarium to prevent the accumulation of detritus, and worse – lingering matter that dissolves and concentrates over time (i.e., – 20% water changes still leave 80% of the undesirable contaminants generated behind to accumulate). Good water flow will keep solids in suspension, which increases feeding opportunities by fishes and invertebrates, and improves filter/skimmer opportunities to export such matter in a well-designed system.

Powerheads are certainly one of the most popular ways aquarists create water flow in the aquarium, yet the technology has its flaws and may not be appropriate for advanced marine systems. They are generally constructed for short to medium-term life, with many being so inexpensively constructed and offered that they are regarded as “disposable”. Some will last more than five years (uncommon), but even they are generally “tired” and only able to provide reduced flow. Most have a useful lifespan of less than 5 years. While we are on the topic of failure and modest construct – what about shock hazards? Good heavens, it is amazing and frightfully common how many people have gotten a shock from a faulty powerhead! Yet it is not actually surprising. Take a look and you will find that most have non-grounded and even non-polarized plug ends that are simply epoxy-sealed into the motor housing. That seal has a limited life… and so will you if you neglect to employ a proper GFI (ground fault interrupter) for your wet aquarium station. What else can we fault powerheads for? Imparted heat – a silent problem inherent with any submersible pump and amplified here by the number of units sunk in the tank to achieve the same water flow as a single cool-running external water pump. For displays with other heat issues (like enclosed and poorly vented lighting systems), powerheads used for primary water circulation contribute more than a few degrees to the water temperature, which can be a serious problem. Of lesser concern but still worthy of mention is the risk that their unguarded intakes pose to aquatic life. Many aquarists have lost animals unnecessarily this way – particularly benthic motile invertebrates, slow/weak fishes, and anemones & toxic sea cucumbers that wait until you go on vacation to drift. Guarding the intakes instead increases the need for upkeep unduly: a small guard clogs quickly, and a large guard runs the risk of becoming an unwelcome nitrifying surface. In systems with high flow needs overall, it may take 4 or 6 or more powerheads to produce the same flow as a single external pump. And at last, power heads are staggeringly unattractive and distracting in the display proper to many observers. Their only saving grace is that they are cheap and affordable, which allows newer aquarists in particular to “buy into” the hobby – a very important and worthwhile distinction.

Depicted here, the rudimentary skeleton of a simple water return manifold. The primary purpose is to offer greater control over the finesse of water flow in the display. Its teed outlets get fitted with fine adjustable aspects – see text below. With this application placed at or slightly above the water surface, one can avoid unsightly powerheads in the display while also reducing their expense and redundancy, beyond issues of poor flow control and excess heat imparted by them. Illustration by Kevin Carroll

This article, however, is not likely to be directed at new aquarists. While the application of a water return manifold is simple enough to construct (and mere dollars worth of plastic for most), concepts of sumps and hard plumbing with valves and adjustable fittings are unfamiliar if not daunting to the truly novice participant. Old, salty dogfish however (experienced aquarists, that is…), have earned honorary degrees in chemistry, carpentry, plumbing and electrical engineering to become reef aquarists. Hopefully, some well-prepared and researching new folks will read this and be spared the gauntlet of powerhead pits just the same. Advanced aquarists are charged to pass the word along in kind if they agree.

Harnessing an external water pump, a manifold of PVC is to be plumbed with a single feed line. [Please refer to the 3-D manifold illustration atop this article for a visual cue to the continued description of its general employ – sump version shown] This feed pipe runs up to the manifold and taps in by a tee. Branching off below this closed loop for any other applications is not recommended; we need a dedicated supply of water here. Obey the manufacturers recommendations for line size. Home aquariums of a couple hundred gallons or less will likely use 1” or ¾” pipe. Larger pumps and systems will use accordingly larger plumbing for this purpose.

The manifold ring/loop of PVC is closed in a complete circuit to help balance the water dispensed from each outlet. Control nozzles will afford the final tuning needed in this regard. Most folks build their manifold the size of the inside perimeter of the display tank. For aquariums with a commercial plastic trim, small holes can be drilled in the recessed lip for plastic ties (cable/zip) to be fished through for securing the suspended manifold. Bare glass aquariums (no trim) can have fasteners (plastic hooks, cable ties, etc) embedded into a dab of silicone near the edge and put to use once the caulk is cured. Acrylic aquariums are very accommodating and can easily be drilled or glued with whatever fasteners work best and are most discreet. Placement of the manifold at or slightly below the water surface (the nozzles at least) reduces or eliminates any issues with salt creep or salt spray.

Tapped into the manifold ring we need multiple tees, angled slightly downward as a good-sense precaution in case the nozzles leak or become “liberated”. The placement of these tees is not of much critical concern as long as you have enough in total to work with; the ability to manipulate water flow through any of them is very flexible and efficient. I’ll suggest 4 to 6 teed outlets per 100 gallons of tank volume, spaced evenly apart, as a starting point. Frankly, you should have no fear constructing a manifold for how inexpensive the framework is to build. In the worst-case scenario, a scrapped structure is a lesson of $20 or less in plumbing, which is a pale and worthwhile investment in light of the value of the display tank.

Next we must decide on the type of nozzle for inside of the manifold tees. They should be movable/swivel… and ideally be able to restrict or regulate water flow. It’s at this point where the project can get as expensive and complicated, or not, as you like. To keep expenses very low, PVC elbows (usually 45-degree) and nipples (short lengths of pipe) are the best way to go. Fittings for small plastic pipe generally cost well under $1 each, or several for a dollar in bulk. A single stock length of straight pipe is like- wise but a few dollars. Short nipples of pipe (1-3”) can be used to connect unglued 45-degree elbows to each teed outlet. The tapered slip sockets of the elbows will afford a snug and water tight seat without committing to a glued position. They can then be swiveled to finesse the dynamic of water flow in the aquarium as corals grow or wane, or when the seascape changes for any other reason. A slight restriction of water flow can be achieved by heating another short
stem of pipe and crimping it to produce a restricted flare-tip that will increase the velocity of effluent water. This modified nipple is to be placed, of course, into an effluent tee. Some discretion is required here, however, as the resistance from a single crimped outlet will likely translate into water taking an easier path of resistance – namely, another open outlet(s). To compensate for this, all outlets need to have similar modifications/restrictions, or valves will need to be installed for each outlet. Valves are not emphasized here as they add considerably to expense, are generally not needed, and complicate a delightfully simple application to excess (creating a “juggling act” with one adjustment affecting all). Another concern is that if the manifold does not have enough outlets, there will be undue pressure placed on the pump (generally harmless for magnetic drives, but perhaps harmful to direct drives). On the opposite end of the spectrum, if too many outlets are
installed (more is generally better/safer for future pump upgrades), they can easily be capped (glued or unglued) with a PVC cap and short stem/nipple. Truth be told, most tanks will be served very well with unrestricted outlets that merely have swiveling 45-degree elbows.

Nonetheless, some aquarists will have more discriminating preferences… and some corals certainly have more demanding needs regarding water flow. This is especially true in display with large or fast growing corals that have a monthly need for modifications in the delivery of water flow. While the above- mentioned swiveling elbows have a very wide range of motion and coverage, there is an even better option: flexible ball-socket joint tubing (wide industrial usage, but found in the aquarium trade at comprehensive LFS shops and online at www.marinedepot.com, and elsewhere). This interlocking pipe is much more expensive per foot than standard DIY PVC parts, but very little of it is actually needed. The product line is complete with numerous adapters for connection to PVC plumbing, as well as add-on fittings to manipulate the ou- going water. A short length (perhaps just 3-6”) is all that is needed on the end of each teed outlet on the manifold to superbly finesse water flow in the aquarium as needed. Clearly, effluent direction on the manifold can be tweaked and tuned in ways that are impossible with rigid and planar powerheads.

Profile of a small reef (36” long – 50 gallon) with a partial manifold (loop is not closed and nozzles not installed yet). Notice the discreet feed through a back wall bulkhead (upper left side of picture), covered by a black shield, fed under the central brace and secured to the obscuring upper front trim of the aquarium with plastic cable ties. Note: the PVC fittings siliconed to rear vertical glass panes are deliberate pockets for corals to encrust upon behind the rockscape for dimension as the tank matures”. photo by Anthony Calfo

Ultimately, the goal with any interpretation of outlets/nozzles that you may choose to employ is to get the outflow paths to converge in the water column to produce random turbulent circulation that is nearly as ideal as surge motion but far less complicated to produce. Dump and surge buckets/devices produce excellent water movement but are generally noisy and inconvenient to install and operate. They are often finicky, and produce problematic snapping and micro-bubbles, and excessive salt creep that is unduly warranted for a home aquarium. They are also cumbersome in size and aesthetically detractive for most living spaces. Such devices are better suited for very large systems, like public displays. Wave-timers with powerheads are likewise inferior to dedicated pumps producing random turbulent flow as their staccato operation increases wear on pumps in use while robbing the system of potential water flow during “off” cycles. Truly, the closed loop manifold described herein produces some of the most efficient water movement in the aquarium while insuring a good value of use (pump life and “bang for your buck” regarding watts used to produce X measure of water movement).

Aquarists for some time have also used external water pumps plumbed directly in and out of an aquarium (no open sump necessary) in a fashion that is called “closed loop”. It lacks a manifold… and actually, lacks any notable means of finesse – it’s simply an external water pump sucking water out of a tank and blasting it right back in. It is crude, but serves a very important role in aquariums with high flow demands that exceed the desired (or able) abilities of a sump path return often hampered by inadequate overflows. [Please don’t get me started on a discussion of the ill-conceived and so-called “reef-ready” aquariums being sold commercially. I still cannot fathom what kind of reef they envisioned with their meager holes/flow rates. Their flow-through capacity is crippling… hello algae!] A closed loop pump on the display, with or without a sump installation, can be harnessed to power a manifold as described above. Since the intake is tapped through the display body wall, and the return is at or above the water surface, there is no risk of an overflow as with a sump from return lines that dip too low and back-siphon in the event of an interruption of power (assuming the safe running sump level was not calculated and obeyed). There is some concern, however, with the protection of the pump intake: it is more dangerous than small powerhead intakes. The literal placement of such pumps is also somewhat to very inconvenient for servicing. It is for these last reasons that I personally prefer to run a manifold off a proper sump pump

With any external pump installation, please be absolutely sure to use flanking slip unions (quick disconnects) and shut-off valves – see illustration. This will allow fast and tidy removal of pumps for cleaning, servicing or replacement. Neglect to heed this aspect of proper installation has often resulted in many hours of hard labor and frustration by aquarists that have hard-plumbed pumps inline and then were faced with draining a tank to remove them.

By category, external direct drive pumps are admittedly not quite as energy efficient as internal magnetic drive pumps (powerheads). But, as previously stated, they are more durable (regarding wear/abuse and lifespan), and they are more powerful (operating against greater pressure/resistance/head). Yet, some modern external drive pumps are remarkably efficient and competitive. They may use less total energy overall than the number of powerheads required to produce the same flow. At the very least, they will save money on spared replacement costs over time (replacement of powerheads) and are safe for the aquarist and its tanks inhabitants at large.

In this article, I hope to have succeeded in bringing to light an inexpensive, discreet and effective DIY strategy for manipulating water flow in the aquarium. If you find utilitarian merit in it, pass it along to a friend and let’s watch such techniques evolve in time.