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Flow-through Live-holding Systems

By Bob Fenner

Automation can be a beautiful (and functional) thing.

When building or remodeling your fish room, three options present themselves regarding how to hold live fishes and plants. This article deals with the pros and cons of these holding systems.

The oldest and most common system is to have separate tanks, tubs with their own independent filtration and aeration set-up, usually undergravel or some sort of box or sponge filter. Second, and growing in popularity, is the concept of recirculating (closed) systems involving mixing water amongst all the tanks of a particular water chemistry and temperature through a central filter/pump. Lastly and newest on the scene, very prevalent among wholesalers, is the industry use of "once through," open systems with new water being constantly added and overflowed to waste.

Initial Cost

Is the initial cost of setting up your store as 1) independent tanks, 2) closed recirculating, or 3) flow-through, non-recirculating less expensive? Which is better in the long-haul?, How long?

There are some substantial savings to be realized by not having each tank independent; some of the major expenses and risks of failure, for individual tank systems is through heater and filter breakdown. These difficulties are much reduced by using system 2 or 3 approach.

A centralized filter system (2,3) may be heated more cost effectively by the purchase and use of a single modern heat exchanger or heat pump using waste heat from your ceiling or outside (even during winter). Depending on your particular application, a gas or electric spa heater or even solar may be appropriate.

Initial costs for systems 2 and 3 include labor and materials to drill and plumb your to an from the filter/drain, pump and related water conditioning equipment. Both techniques, 2 and 3, cost about the same to set up, to provide a water heater, or two in series, a needle valve drip system and waste lines from your tank. Money is saved using the flow-through system by using city water pressure to deliver new water into your tanks instead of pumping in the recirculating option.

Depending on the relative costs of electricity and "usability"/cost of water, these systems may be more or less costly up-front.

Operation and Maintenance Costs

Individual tanks require weekly or more frequent vacuuming, refilling, changing, cleaning filter media and checking of water chemistry and temperature. More having to "fool with" your tanks results in greater stress on your livestock, and consequently, more mortality and less profits.

Recirculating systems vastly reduce the need to vacuum your tanks, tanks are automatically topped off, there is less need to change filter media in your central filter, and water quality changes rarely fluctuate in such a large body of water thereby eliminating vac-ing, filter cleaning and heating problems.

Labor costs (your number one cost) saved not having to continuously clean aquaria, presenting a picture to the buying public of a drudge-ridden hobby, are to some degree reinvested in maintenance of recirculating pumps, added electrical costs in some cases, water conditioning and mechanical parts check and replacement.

Health and Disease Considerations

A major concern for all retailers is maintaining the health and appearance of live stock. Probably the major cause of fish loss is poor water quality: e.g. high ammonia, other organics, low oxygen, fluctuating, high or low pH, brought on by over-crowding, and/or not frequent enough water changes. These problems can be greatly reduced by the recirculating or drip systems. Recirculating systems do this by spreading out the biological load throughout the system. Once-through drip systems do this by flushing out wastes continuously.

As stated before, most captive fish losses are due to poor water quality. Many people are rightfully concerned about spreading infectious and parasitic organisms through a mixed water system. This need not be any greater problem than the risk of cross contamination via nets and specimen containers in an individual tank system. In the most recent stores, we've put up with central re-circulating systems., a 20 micron cartridge filter, followed by an appropriate strength ultraviolet sterilizer has been incorporated so successfully that environmental and biological disease have been all but eliminated. Of course, on introduction, we take pains to use sterilizing dips and discard all shipping water.

On saltwater pump systems, we've gone the extra distance to use an in-line protein skimmer and ozonizer that goes a long way to reduce organic concentration and color. With reduced synthetic water changes and organism losses, we've found this expense to be well worth it in the immediate short-term.


The particulars of sizing, flow rates, design and engineering are a function of several cost and availability factors for your area. Check around in your area or towns you visit on vacation or trade shows as to set-ups of other successful retailers

The principal question that we ask when presented with a chance to build or refurbish a fish section, is what do you want this system to do and how much time and money do you want to devote to this part of the project? If you have little ready time, cash and don't mind losing more livestock, cleaning tanks more frequently by hand, and having your aquaria not look their best, the traditi8onal single system per tank approach is for you. I predict that the future belongs currently to re-circulating systems and probably drip systems in the very near future. When you size up the initial operation and maintenance costs with the few months time that it takes to recover these costs and all the overwhelming benefits, there is small comparison with having a self-contained, self-maintaining flow-through system.


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