Book Review: Aquatic Systems Engineering: Devices and How They Function

This is a review of the new CAS library book, Aquatic Systems Engineering: Devices and How They Function, by P.R.Escobal. The author is an aeronautics engineer that left the field to form the companies Aquatronics and Filtronics, manufacturers of “high-end” aquarium filtration, aeration, and sterilization equipment.

The book discusses the use of these items in setting up an aquatic environment: both single tank and multi-tank systems. The proper sizing of components is discussed in detail, and mathematical rigor is used. This book is therefore not light reading: in fact, tables, schematic diagrams, and calculation make up the bulk of the book.

The calculations are however complicated by the exclusive use of American Imperial units throughout the book, rather than the much simpler SI units. As the author is American, this is understandable, but even American engineers will nowadays calculate in SI and (if required) convert the result to antique units after it is found.

After an introductory chapter that defines the terms used throughout the book, the meat of the book begins with a surprisingly complicated discussion on how to determine the time required for passing all of an aquarium’s water through a device (such as a filter). The complication arises from the fact that the water from the filter is mixed with unfiltered water on return to the aquarium. It is shown that all of the water can never be filtered in such a set up, but 99.99% of it is effectively filtered after the volume of water is cycled through 9.2 times. One can safely round this to 10 times, and say, for example, that a 100-liter per hour filter would require 10 hours to filter all the water in a 100-liter tank. The commonly used aquarist “rule of thumb” is to use a filter that pumps the aquarium’s water volume two to three times per hour, reducing the filter time to about four hours.

The next chapters deal with the proper sizing and operation of ultraviolet sterilizers. It is here that the author shows his biases. Chapter three opens with the sentence “Fishwise, the single most important device available today, ranking second only to a well designed mechanical filter system is the ultraviolet sterilizer”. Even setting aside this statement’s self-contradiction, I find this declaration odd to say the least: the vast majority of successful amateur aquarists don’t even use an UV sterilizer so they clearly can’t be that important. And the mention of a mechanical filter I also find odd, because I only use them as a prefilter to my biological filter, which I would surely rank as the most important aquarium device anyone can have.

If the opening statement was meant to boost sterilizer sales then I am afraid that in my case, at least, it has failed, since the contents of the sterilizer chapters have convinced me not to buy one. The discussions on “dwell time” and “zap dosage” clearly show the futility of using a small UV sterilizer in a moderate to large sized aquarium system. For example, a 25-watt UV sterilizer (itself costing about $250) can only be useful on a 180-liter or smaller aquarium, and then only if the flow rate through the sterilizer were carefully regulated. My 500-liter show tank would require 64 watts of UV to be effectively sterilized at a cost of nearly $1000 (including pump, flow monitor, and plumbing). Since I have never seen any of the diseases that UV sterilization is supposed to prevent, this expense hardly seems justifiable. However, to anyone deciding on using an UV sterilizer, I would say that these chapters are required reading, as they convincingly demonstrate that careful matching of the tank capacity, sterilizer wattage, and pump flow rate is required for satisfactory results. You simply can’t stick any old sterilizer to the output hose of your canister filter and expect effective sterilization.

The following chapters discuss the design and operation of protein skimmers, and should required reading for anyone wanting to design such a device.

There is also a chapter that discusses heating and cooling of aquaria. Heat loss from a model aquarium is examined and examples are given as to how to determine the heater wattage needed for a given tank. This information is potentially very useful, but unfortunately it doesn’t adequately address all the complications that arise from extraneous heat coming in from the lights or water pumps, or the complex configurations of multi-tank systems, or of open-air tanks that suffer from evaporative heat loss. So in the real world, you would still probably have to rely on trial and error when sizing a heater for a multi-tank system.

Two points do however become quite clear while reading the chapter on aquarium heating: acrylic tanks require much smaller heaters than do glass tanks, and
“watts per gallon” heater sizing rules are useless. Heat is lost from the tank proportionally to its surface area, not its volume. So even though beginner books may advocate buying a heater big enough to supply “5 watts of heat per gallon”, and even though this may be fine for a 10 gallon tank (50 watts of heat), it results in serious overkill in 100 gallon tank, where 500 watts of heat will cook your fish.

The chapter discussing water pumps is also informative, but is hampered because it discusses pump performance in terms of output pressure. Unfortunately pump output pressures are almost never given for hobbyist pumps. Instead, pumps are rated by flow rate…either at a variety of “heads” (if you are lucky) or as a single value. The pump “head” is the height the water is lifted by the pump, but many aquarium pumps are designed strictly for “flat flow”, or zero head. Such “circulation pumps” are only given a passing mention.

For those pumps that are rated for pump flow at various heads, it is easy to determine the pump pressure, but the relevant equation is not provided in the book. So here it is…let

P = pump output pressure in Pascals.

z = be the height in meters where flow rate drops to 0 (the maximum head).

d = density of water (which is 1000kg/m3 for fresh water)

g = gravitational acceleration (which is 9.8 m/s2 near the Earth’s surface)

then P = d g z

= (9800 kg m-2 s-2) z

To convert pressure in Pascals to PSI, multiply the pressure in Pascals by 0.000145 PSI/Pa. You can also make a quick estimation of the pressure by remembering that every meter of head requires the addition of about 1/10 of an atmosphere of pressure, where 1 atmosphere is about 1000 Pascals or 14 PSI. For example, my pond pump is reported to pump to a height of 8 meters, so it must deliver about 11 PSI.

Once the pressure of the pump is determined along with the diameter of the pump outlet, the flow rate at any head is easily determined from the formulae presented in this book. But much more importantly, the book also presents the information required to allow you to design a real filter system, taking into account the losses of flow due to friction in your hoses and connectors.

This information is to my mind the most universally applicable information in the book, as the most complicated piece of “aquatic engineering”” that the advanced hobbyist is likely to attempt is a single-pump, multi-tank fish room. Everything you need to know about sizing and designing such a room is included in this book, and I don’t think anyone should attempt it without first having a thorough read. ?