6. WATER FLOW IN THE REEF TANK:
Any hobbyist who has kept aquariums for a while, and any hobbyist who is just starting off, knows or has heard of the importance of water circulation. Turning over water, or turnover rates per hour, as it is called, is dealt with in many articles in hobby magazines and books. Suggested turnover rates vary from a low of three times to a high of eight times the content of the aquarium, per hour. All indicate, or so it seems, that such is necessary mainly for filtration and oxygenation purposes. Which is of course true, but only partly so.
What is overlooked in most cases, is the fact that water circulation for filtration purposes is only one form of necessary water circulation. The second, and perhaps as important one, the one usually not mentioned, is the "current" or water movement inside the tank, which is required by all invertebrates and corals, because such is exactly what they are accustomed to around the real reef.
There is a great difference between the two. Current can be obtained by placing, for example, power head type pumps in the aquarium and directing them at certain angles to ensure that all areas of the tank experience moderate to strong current. This setup can then be improved upon by alternating the on and off cycles of those power head pumps with a device that periodically changes the electrical current going to each one at preset intervals, making it a cyclical and recurrent pattern, just like in the ocean around the reef.
Commercially sold devices to achieve this are now available in pet stores and from reef specialists such as Thiel*Aqua*Tech, about the only company making it a strong point of their technology to bring out equipment that allows hobbyists to keep their stock alive for much longer periods of time, thus contributing, albeit to a small degree only, to the preservation of the natural reef and a reduction in its depletion. Other companies include Route 4 Marine Technology, Lifereef Systems, and Marine Technical Concepts.
Water circulation for filtration purposes is achieved by means of "circulator" pumps and need not be as high as the levels sometimes indicated in literature, as long as the hobbyist provides strong current inside the tank as well. Two to three times the content of the tank per hour, is plenty, in my own experience.
Because the life forms you keep depend on the quality of the filtration (especially the biological one), care in selecting a good quality circulator pump is a must. Too many hobbyists buy the cheapest pump they can get away with. Such is a mistake. Your circulator pump must run hour after hour, day in and day out, for months if not years, without failing you. This requires a pretty decent piece of equipment, not just any pump.
Remember, when your pump fails no filtration takes place, and your filter bed - the bacteria - may die within a matter of hours, or sooner, depending on what type of medium you are using inside your trickle filter. Plastic media give the best survival rates. Bio*Techs, Super*Techs, Bio-Blocs, Bio-Cubes, Bio+, Mini Balls, Jaeger Tri-Packs, and so on, are all excellent media to use inside your trickle filter's biological chamber, and can weather longer power outages or pump breakdowns.
Buy a pump that can withstand this tough service, one that has been made for continuous use in salt water aquariums. Most pumps sold in the hobby are chemical pumps used in other industries, and offered for sale in the hobby. Iwaki pumps, for example, come for the most part from the photographic processing industry. Although they are excellent pumps, they run a little too hot in my opinion. I no longer use them.
Sizing the pump is another area of confusion. Hobbyists use the following rationale: "my tank holds 100 gallons so based on what I have read, I need a pump that can move 300 to 400 gallons of water per hour". Such is wrong. The output of pumps is given at zero feet of head pressure (no back pressure on the pump, or said simply, not taking into account that the pump has to push several feet up, and through pipe or hose that may be going at many different angles). Height, fittings, the type of pipe used, all influence the pump's performance, and can reduce that output considerably.
To achieve the actual 300 to 400 gallons per hour that the hobbyist set out to achieve, he or she will more than likely need a pump that is rated at 800 to 900 gallons per hour. Make sure you keep this in mind when you select a pump for your own system. Spending money on a pump, only to have to change to a stronger motor a couple of weeks or months down the road, is really a waste of money, and time.
Make sure too that all parts can withstand being in saltwater for extended periods of time, and that the pump you buy is rated for continuous use. Saltwater safe pumps should not contain any parts that are not totally salt water resistant. This means that the pump housing and inside parts need to be of a durable inert plastic, or 316 stainless steel. Brass, zinc, monel, and so on are not acceptable. Keep in mind as well that you may be using ozone. Ozone will make any material deteriorate very quickly, unless you have a real high quality pump. I am not suggesting that you should buy a pump that is rated for ozone service. Such would cost you over $1,200, but you should get the next best thing, usually a pump with totally enclosed magnetic drive parts, casing made out of Kynar or virgin, (not mixed) polypropylene, impeller out of the same materials or 316 SS, Viton seals, and so on.
Additionally, you must know that many pumps cool themselves by transferring heat to the water. This increases the temperature of the water in your tank by several degrees, which is not desirable at all. Keeping the water in your reef tank low is a big enough problem as it is. Get air-cooled pumps for your tank. They are sometimes referred to as blast-cooled.
Clean your pump(s) from time to time. Dirt, slime, algal debris, and so on, get inside the impeller chamber whether you like it or not and all impede the water flow. Besides, they may even build up to a level where the pump is being damaged and runs warmer because it has to labor harder to push the water through the pipes. I suggest you clean your pumps at least every 10 to 12 weeks. More often will, of course, not hurt.
To do so, you must take into account, when installing your system, that you will need to be able to take the pump out of service from time to time. The only way of safely doing so, is to install true union ball valves on each side of the pump. You can then shut off the valves when you need to service the pump, and remove it from the lines easily without much water spillage each time it needs servicing or cleaning. True union ball valves are somewhat more expensive than plain shut-off valves, but because of the union part they can be opened, the pump moved out of place and cleaned, and then re-installed. Once you have done it a few times the whole process should not take you much longer than 10 to 15 minutes.
Pumps come with in and outlet size fittings deemed best by the manufacturer to operate their pumps efficiently, and obtain the water movement ratings listed on the specification sheets. Although you can downsize the outlet side of the pump, or install a ball valve in-line to regulate the flow and service the pump, you should never ever downsize the intake side of the pump. Doing so may not bring enough water inside the impeller chamber and cause the pump to "cavitate" and break up the water so forcefully, that all dissolved gasses come out of solution. You then end up with a myriad of little air bubbles in your tank, you place a lot of strain on the pump and may ruin it, and you will heat up the water considerably. Besides, the tank will look very unsightly. If the intake side of the pump calls for one inch pipe or hose, keep it that way, if the intake is half inch, keep it that way as well. Do not, under any circumstances, change the intake size by changing the hose or pipe size.
Always buy a pump with a rating much higher than what you have determined your need to be. For example, in a 100 gallon tank, with the filter underneath the aquarium, and a moderate amount of 90 degree elbow fittings to bring the water to the tank, you should use a pump rated at zero feet for about 900 gallons per hour, or about 600 gallons per hour at 4 feet of head. You will probably end up with a true 400 gallons per hour going through the tank.
Such is about what you really want, because you can now adjust the exact output with the ball valve you installed, until you are comfortable that the water circulation is adequate for your 100 gallon aquarium.
Although I can recommend how much greater than your need the pump you buy should be, I can only do so after I know more about the exact manner in which the hook-ups are done, and how much "head" the pump will have to push. Generalizing is usually not a good idea, since such does not apply to everyone. Moreover, some pumps are good at overcoming head, and others are not. Circulator pumps can usually not handle a great deal of back pressure and lose their output very quickly as a result. All this complicates the picture somewhat.
My recommendation is therefore to first determine the approximate head that your pump will have to push, and then to specifically ask the output at that number of feet from whomever you are buying the pump from. Compare that number to the flow you want and decide whether or not to buy that pump.
How do you calculate the head? You can, I have to admit, not calculate it accurately unless you have access to special manuals and understand fluid mechanics. You can, however, take a pretty good guess at it, and you will usually be very close.
First measure the number of feet upwards that the water has to travel. If you are returning the water through the bottom of the tank, you must measure the height of the water column in the tank as well. Count the number of fittings used, excluding elbows (If you are not familiar with fittings, see later in this book for more details on PVC fittings and valves). For each fitting that you have used, add 1/5 foot of head. For each elbow used add ¼ foot of head. Add 1 foot for the pipe, and add 1 foot for the valves used. Head can, as you must have realized, build up quickly!
As an example: a 55 gallon tank, with water being returned from the top. Height to top of aquarium, including stand is 4 feet. 3 fittings and 2 elbows are used. The pipe size is half inch (same size as the output size of the pump). 2 ball valves and 1 check valve are used.
Rough head is: 4 + 3/5 + ½ + 1 + 3, for a total of 9 1/5 feet.
Now that you now the approximate head that the pump will have to push, determine what the output of the pump (and brand model or number) you are thinking of buying is at 9 to 10 feet. Does that match the amount you had determined that you needed for your tank? If yes, and the pump meets all other criteria set, buy it.
Another factor to be reckoned with is that heavily loaded small tanks need higher amounts of flow through the filters. For a 55 with a heavy load, 200 gallons per hour, plus good extra circulation inside the tank by means of power head pumps, is a must. If you do not install power head pumps that number needs to be increased to about 275 gallons per hour.
Noise is another factor to take into account, especially if your tank is in your living room, and most are. Manufacturers do not, as a matter of course, give noise ratings. Talk to a friend, a pet shop, the aquarium society in your area, or another equipment manufacturer to find out more about the noise generated by some of the pumps offered for sale in the hobby. Several real quiet ones, and a few very acceptable ones are available to the hobbyist. Because we assemble our own pumps, TAT models fit all criteria outlined in this chapter. So do the modified Grundfos 4500 3-speed, and 6400 1-speed stainless steel pumps we sell.
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