Controlling Fish Tank Diseases

Disease in the aquarium is one of the main fears of aquarists. Once the presence of a disease is known the aquarist’s stress level shoots up and quite understandably so – at the worst there could be a full aquarium wipe-out.

When the word disease is mentioned most straightaway think of fish, but it is not only fish that could have problems, it is corals too.

I’ve not got any magic formula that will ensure that disease will never appear. What all aquarists do have available to them is straightforward common sense.

The very first requirement in building a wall to defend against disease is the aquarium system itself. Design in other words. Everything should be dedicated to the overall needs of the system, and that is stability and seawater quality. They go hand in hand anyway so it is likely that one will give the other. The heaters employed should be able to maintain the temperature with a low variation, say + or – 1 deg F. The powerheads that drive the seawater circulation should turn it over sufficiently; the guidelines are around 10 times the net gallonage of the display aquarium per hour for fish only and soft coral systems, and around 20 times the net gallonage of the display aquarium per hour for hard coral (SPS) systems. In addition, the seawater movement should not be linear, but should be random and chaotic. Sufficient seawater movement will also ensure that there is enough oxygen – a very important point. There should be a quality protein skimmer that is known to be capable of handling the net gallonage of the system. The aquarist could consider the use of a UV filter, which will kill or severely damage parasites exposed to the light (some use them, some not, but they are useful though not a complete answer in themselves).

The bio-filter, that is the filter that houses the indispensable bacteria that rid the aquarium of toxins (ammonia and nitrite), should be efficient and of an adequate size to deal with the aquarium bio-load. There should be sufficient live rock if that is the aquarist’s choice, and it should be of sufficient quality. In a reef system the reef structure is often completely constructed of live rock and so should be adequate, particularly as the fish load is less to preserve seawater quality. However, in a fish only system a full reef may not be constructed so care needs to be taken to ensure the quantity is adequate, particularly with the normally larger fish load.

If the aquarist uses a canister or similar as the bio-filter then it needs to be large enough to cope with the size of the system and its bio-load – in other words, it must be capable of moving sufficient seawater through enough bio-media.

In the case of a reef system, the lighting should be adequate for the corals, giving an adequate spectrum and intensity, and consideration should be given to the depth of the aquarium with regard to light penetration.

When the aquarium is up and running, the aquarist must be sure that the bio-filter is ‘mature’, that is, it has sufficient bacteria present to deal with the bio-load. The bio-load itself should be increased slowly, particularly with fish, giving time for the bacteria to adjust to the work facing them.

Selecting livestock is the next line of defence. When corals are selected they should be judged very carefully when still in the sale aquarium, and they should be compatible with the system and their intended neighbours. The same applies to fish – before purchase the aquarist needs to ensure they will be compatible with the aquarium system type (reef or fish only). There are texts available advising what to look for, including on

The stocking level of the reef or fish only system should not be exceeded. Temptation could arise ‘down the line’ when all is well. Why not put one or two more fish in, what harm could it do? It could be a step too far, beginning a slow deterioration in seawater quality and an increase in aggression among fish or corals.

Ongoing quality husbandry, that is maintenance of the system, is essential. Maintenance is sometimes the first thing to deteriorate, because all looks well and missing this or that just once or twice surely won’t matter! It’s the beginning of the slippery slope to problems including potential disease because of diminishing environmental quality and should be avoided. Routine seawater changes should be completed. The protein skimmer should be cleaned at least once, better twice, a week. Mechanical filter media should be cleaned. Pumps and powerheads should be checked to ensure continuing adequate output. Activated carbon, anti-phosphate resin and the like should be renewed on time. The same goes for lighting tubes or bulbs.

Feeding should be adequate for the dietary requirements of the livestock. Feeding should not be overdone – overfeeding is one of the causes of poor seawater quality which could and often does mean trouble.

The major concern in anti-disease efforts should be prevention, the best control of all. If the livestock are not stressed because everything is supporting a high quality environment the danger of a disease outbreak is reduced. There is the danger of a disease problem being introduced with livestock, and it is the aquarist’s knowledge and careful eye when selecting inmates that is the best guard against this.

The marine hobby sometimes seems complicated with all the equipment available, the different systems and the different livestock that could be introduced. The basics however are not complicated and only require a little effort to understand and follow.

  1. This is good, simple but accurate information. Many thanks.

  2. I’m pleased that you found it so.

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