So often I am asked ‘what will I need to get to have a salt water aquarium’? My answer is simple, funny but true: ‘Saltwater and an aquarium’. If you really think about it, that is all you need to have a saltwater aquarium, saltwater and an aquarium. Depending on the size of the tank, an empty tank of saltwater will probably support a small species of local marine fish. The waste produced from this small fish will support cultures of bacteria which will grow on the glass of the aquarium and break down the waste from the fish. Algae is then likely to form on the glass, giving the fish an extra source of nutrients and oxygen. Providing the fish is fed almost nothing, it is possible for saltwater and an aquarium to support this small fish even long-term.
The problems will start to arise once you start to add more fish. More fish means you will have to start adding more food. Once you are introducing more food then the natural capacity of the bacteria and algae that grow on the glass will be inadequate. If this is the case then the biological breakdown of the food will create toxic conditions which will kill some or all of the fish until a balance is restored. Nature is all about balance. If we have too much waste being produced for the capacity that we have to break it down, then this unbalance will naturally be balanced by nature by killing the fish responsible for this unbalance.
What you will learn in this article is that the unfair bit about aquarium-keeping is that the unbalance is really not the fish’s fault at all, but the aquarist`s. All aquarists must understand this natural balance and what affects it.
Consider that our fish don’t produce waste and that all the waste is produced by you. You are the one that feeds the fish and all the waste in the aquarium is a direct result of the food you have introduced to it. A fish eats the food and the system breaks down the waste - it is all a game of balance. If your system cannot break down the amount of waste that would be produced by the amount of food that you need to feed to support the amount of fish that you have, then you have an imbalance. You will need to reduce the amount of fish that you have or increase the capacity of the system.
To determine how many fish a system can support, we must look at the most limiting factors of the system. Let’s go back to our empty aquarium with saltwater and one suitable small fish happily living in it. If we wish to add more fish we need to look at another limiting factor, the most obvious one being oxygen. By simply increasing the oxygen level of the water, we dramatically increase the capacity of the system. This is mainly due to an increase in what is known as the redox potential of the water. The redox potential is a measure that relates to the bacteria’s ability to oxidize (break down) waste in the water. Anything that will raise the redox potential will increase the capacity of the system. The introduction of oxygen will allow bacteria to work much faster at breaking down the waste in the water.
The oxygen level of an aquarium is increased by anything that causes the water surface to be broken. Unbroken water surface will form a type of laminar which will allow very little oxygen transfer from the surrounding air into a body of water. When this layer is broken and the oxygen is able to penetrate, the capacity of the system is increased.
The surface can be broken using vertical or horizontal methods. The vertical method is the use of an air stone which will create bubbles to break the water surface tension; the horizontal method uses water pumps to agitate and break the water surface. Vertical methods are rarely used in most reef aquariums as they can only produce a limited amount of water flow and the constant popping bubbles will spray salt all over and create more annoying salt creep. Most reef aquarists aim to have 14 times per hour water flow. If you have an aerator running while you have that level of water flow, then the tank is likely to become white with micro bubbles.
The next limited factor would be surface area for bacterial growth. The reason why surface area is so important is because the larger the amount of surface area you can provide, the more bacteria you can grow. Growing more bacteria allows for more fish which produce more waste.
The best and most natural media to increase your bacterial capacity is live rock and coral sand. Live rock is the calcium carbonate structure left once a stony coral dies, while coral sand is produced when fragments of this rock break down into sand. This rock has a porous consistency which allows the formation of different types of bacteria, algae, corals, and micro-organisms. Decorating your empty saltwater aquarium with live rock and coral sand will give you an amazingly massive surface area for bacteria to grow. Surrounded by water rich in oxygen from pumps creating 14 times per hour waterflow, you will now have an amazing capacity to support fish. It is surprising how many fish a system can support when decorated with live rock and coral sand.
So let’s check in on progress, we now have a fair amount of fish that need to be fed, living in oxygen-rich water. Food is eaten by the fish and organic waste is produced. This waste is then consumed by micro-organisms, algae and bacteria in the system leaving mulm, and potentially nitrate and phosphate. Mulm is non-organic detritus that is not able to be broken down any further; nitrate and phosphate are low-level wastes not always able to be totally controlled by the natural biological breakdown of a system with a large load of fish.
The inclusion of regular water changes using a gravel-cleaner would be a great next step. A gravel-cleaner will allow you to vacuum the coral sand of your aquarium and remove the mulm from the sand while performing a water change and diluting your possibly elevated nitrate and phosphate levels. The amount of fish that you have will directly effect how often this should be done. You can see how dirty your sand is and test your nitrate and phosphate levels to determine how often a water change needs to be done. The water change is a perfect time to remove this mulm from the sand to stop it building up to the point where it may create toxic hydrogen-sulfide in the aquarium.
There are also nitrate and phosphate sponges and resins that can be used to control these levels. The amount of algae you get in your aquarium is directly linked to the level of phosphate in the water.
The next factor to consider for this aquarium is light. In this current aquarium, depending on water quality as a result of fish load, you may choose to start adding corals to the tank. Some corals can be added directly to the tank considering that some corals don’t even require light at all, while other shallow water corals will require a very strong light of at least 1watt per litre. The inclusion of a light with this aquarium will allow a tank which is predominately fish only to become a coral reef aquarium. Most tropical coral reef aquariums need to be run at 25’C so you may need to consider running a heater and/or a chiller to maintain a stable temperature.
Note at this point we have a thriving reef aquarium with all type of different fish and coral and we have not added even talked about adding a filter of any type whatsoever.
This aquarium that we have now set up will have an amazing capacity to keep all sorts of aquatic animals over a period of time, but over that long period of time other features such as trace elements and quality of food will affect some species.
Many coral require various trace elements which if not provided will result in the death of the coral. Water changes will help to replace trace elements but only enough for a small stock of coral. Trace elements tend to only stay in solution for a short period of time, so they should be replaced at least weekly in order for it not to be considered as a limiting feature long-term. Trace elements have a massive effect on the immune system of both fish and coral over a long period of time.
The next thing to consider is quantity and quality of food. The fish must be fed enough so that the average fish has a small belly. If several fish are fat then you need to reduce the amount of food, if several are skinny then you need to increase the amount of food.
The higher the quality of food, the better the long-term results you will see with the fish. Variety does not equal quality; you should focus on quality over variety. I am very biased toward ‘New life spectrum’ food. It produces amazing colours in the fish and creates very little waste in the water. High quality foods are designed with certain ratios of various nutrients, vitamins and trace elements so that the food is evenly absorbed by the fish producing very little waste. Lower quality food may deliver lots of one requirement e.g. protein while lacking most other requirements. This will mean that the required protein is stored by the fish and the rest is expelled as waste.
Aquariums containing fish correctly fed on high quality food will contain healthier fish with stronger immune systems with lower nitrate and phosphate levels in the water.
At this point we will now discuss the idea of adding a filter. The most common type of filter on a marine aquarium these days is a sump filter, which can go in the cabinet under that tank. This is simply because it is a great place to hide all of the hardware. Many types of filters are effective but I am biased towards the refugium-style sump filters, which use a plenum under a deep sandbed to increase bacterial capacity of the aquarium. Other media can also be used such as Matrix or more live rock to increase biological capacity. In the early years of marine keeping the bio-ball was a big hit, but they are outdated compared to more modern media which don’t allow as much nitrate in the water.
The water flow of the aquarium of 14 times per hour does not mean that that amount of water has to go through the filter. Consider that 14 times an hour is the aim for the aquarium, while much less than that needs to pass through the filter to allow a beneficial contact time between media and water volume, more like 5 to 6 times per hour. Also consider that the water escaping the filter is often very low in oxygen as much of it has been used for oxidization by the bacteria in the filter media.
Another old favourite in the marine aquarium hobby is the Protein skimmer. This device will skim organic waste out of the water, allowing a larger biological capacity to be maintained in the water. In any highly stocked aquarium this bit of equipment is worth its weight in gold, as it is able to increase the redox potential of the water and therefore increase oxygen and biological capacity.
An ozonizer can also be added to the system via the skimmer allowing an even higher capacity again. It is truly amazing the amount of fish stock that you are able to support with the use of this equipment, all maintained healthily in crystal clear water. The ozonizer will also perform functions of a UV sterilizer, which decreases the chance of fish becoming sick due to parasitic infestation and so is very beneficial in aquariums with massive bio-loads.
There is no end to what is possible in this hobby which is as diverse as an aquarium with salt water and one fish to massively stocked tanks housing every type of fish and coral that you can imagine run by a complicated life support system.
To anyone considering getting a saltwater aquarium my advice is to get out there and start. You will be continually amazed by this extraordinary hobby even if you are just starting with an aquarium and some salt water. You can grow it as slowly as you want, but don’t forget that it is all about balance. Nature demands this balance, its all about how many fish can you have in a body of water that need to eat an amount of food to produce an amount of waste which will need to be broken down by an amount of bacteria.
Good luck and enjoy.
Paul Talbot
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