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When you're designing a large-scale custom aquarium system, a number of issues should be relatively simple. Before we delve into the details, let's take a look at some of the broader general concepts.
General Design Goals
You have to design a system that will accomplish specific goals. The first, and most obvious goal is to provide an adequate artificial habitat for you fish, plants, and invertebrates. Less obvious, but equally important design goals are that the system be reliable, fault tolerant, and cost effective. Failure to plan for a reliable, fault tolerant, cost effective system will likely result in a system that is failure and disease prone, subject to catastrophic failures during power outages or other events, and which costs more than it needs to.
Designing For Reliability
The major characteristic of a reliable system is that the system components do no fail to meet specification on a consistent basis. There is the expectation that a reliable system will perform day in and day out in an expected manner. Several ways to accomplish this goal are as follows:
- For structural components subject to static forces, expect that there is a 30% variance in the strength of the material from the production specifications. By increasing your requirements by 30%, you ensure that even if you use a component that is at the lower end of his variance, it will still meet your specifications. Structural support members that do not take dynamic stress and strain can be considered in this category.
- Structural components subject to dynamic stress, such as the glass or acrylic which may take additional dynamic stresses during filling, should be sized upwards by 100% in addition to accounting for manufacturing variances. Since it is impossible to fully anticipate the full range of potential dynamic stresses it is a good principle to overcompensate for these forces.
- Plumbing and filtration systems will accumulate detritus that can easily reduce subsystem efficiencies by 50%. Ensure that the system design can adequately handle anticipated loads when operating at half efficiency, and upsize these components as necessary.
- Plan for potential upgrades and modifications. If you believe it is possible that you would add filtration components at a later time that will require additional flow capacity, it's a good idea to install larger bore pipe at the outset so you won't have the potential problem of running those systems on an undersized plumbing system later on.
- Spend money on sealants. These potential failure points are relatively inexpensive to protect and are the cause of a large percentage of tank failures.
Designing For Fault Tolerance
Fault tolerance allows a system to continue to operate if a failure occurs, or to at least prevent catastrophic failure if a system fault occurs. Fault tolerance must be planned for the failure of components within the system, and for external effects, such as power failures, happening outside the system. While fault tolerance can increase the system cost, it can prevent the occurrence or minimize the effects of failures that could wipe out the tank population. A few examples of fault tolerant design are as follows:
- For water returns that are below the aquarium water level, install a check valve to prevent a backflow siphon effect during a power outage that would potentially empty the tank.
- Consider battery backup for heaters and/or biological filtration systems to prevent die-off during power outages.
- In electronically actuated plumbing subsystems, consider the effects of "normally open" (NO) and "normally closed" (NC) switches and valves and select the type that has the least potential for catastrophic failure.
- Install a grounding probe to prevent safety hazards in case of an electrical short.
- The potential for failure in dual parallel systems is halved, for those in series doubled. Solve potential problems in series systems first.
- Consider all sources of potential failure, and find ways to mitigate effects giving priority to those that are most significant, and then to those that can be inexpensively resolved. There is little excuse to planning for a major catastrophe, and none at all for a failure that could be averted cheaply.
- For contingencies that cannot be effectively averted, place an alarm system that will allow timely user intervention.
Designing For Cost Effectiveness
The temptation in design is to oversize everything, but not only is this ineffective or possibly ill-advised in some instances, it adds unnecessary expense. Many of the "rules of thumb" that are commonly in vogue end up oversizing components and adding excess costs. It is far better to make as accurate a calculation of your requirements as possible and meeting those requirements, than to heavily oversize those requirements "in order to be safe." In many instances where this is done, the additional expense of meeting these overstated requirements comes at the cost of implementing fault tolerance or other important design goals. In other instances, by using the most effective configuration of components we can reduce the system requirements themselves and have a more efficient system. Here are some ways to improve system cost effectiveness:
- The more square a panel of glass or acrylic is, the stronger it needs to be. If possible, size your panels to be rectangular where possible.
- Most friction losses in pipes are due to fittings and valves. Minimize their use as much as possible, and avoid the use of inefficient valve types such as globe valves.
- Fitting and valve friction loss data is provided for these components in isolation. If these components are used in close proximity to each other excessive turbulence may cause additional unplanned friction losses which may require system redesign and rebuild. Separate these components as much as reasonably possible, even if this requires additional piping.
- Schedule 40 PVC pipe is effective, inexpensive, and easy to work with.
- Not all sides of a tank must be see-through. It is much cheaper (at least 90% cheaper) to use marine grade plywood for hidden sides and go to the trouble to bond them to the glass or acrylic.
- Planning for a tank overflow to supply water to the filtration system is cheaper and more efficient than plumbing a siphon.
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