Moving from a freshwater tropical tank to a marine aquarium 

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Marine aquariumWhile keeping a freshwater tropical tank can be an incredibly rewarding experience, many aquarists often aspire to have a marine aquarium too, but are sometimes put off by horror stories about how much can go wrong!

In truth, experienced marine aquarists will tell you that there is much more to think about, if you have previously kept just a typical tropical tank with little in the way of plant life, but they are also likely to tell you how worthwhile it can be!

Thankfully, the fundamentals of marine fish keeping are just the same as tropical – look after the water, and the water will look after your fish, but there are a few differences that you need to take into consideration from the outset.

The nitrogen cycle

Fiji blue devil damsel  Chrysiptera taupouBroadly speaking, the nitrogen cycle in your tank will remain roughly the same, at least on paper. Fish are fed food, which produces waste, and this is broken down from ammonia into nitrites and then nitrates – nothing new there then, but because of the extra chemicals involved in marine fish keeping, things can sometimes go wrong very quickly.

Bear in mind that it might take a marine tank a little longer to mature fully, so consider using filter start bacteria to get things moving early, with fish-less cycling being essential at the outset. You should never rush to purchase fish until the water conditions are stable and suitable. It is also best to start out with relatively tolerant fish, such as members of the damsel group, as shown above.

Salinity levels

ClownfishWhile your freshwater tropical tank will of course have a salinity level, this figure will be low, pretty static and only fluctuates a little, providing you are treating your tap water consistently. In a marine tank however, salinity obviously becomes a much bigger issue.

We recommend that you are consistent with your choice of marine salt, making the decision early on as to whether to include live rock and corals in your tank so that you can use and stick to a reliable brand of reef salt that will be ideal for your tank's occupants.

A refractometer is also a great investment, allowing you to test batches of fresh top-up water as well as your main tank water at a glance. This should serve to ensure the salinity is at the optimum level to support the healthy lives of your fish and any invertebrates, as with the clownfish seen here which have a close relationship with particular sea anemones.

Trace elements

Getting to know the trace elements needed by the fish and corals in your marine tank is also a great idea. Marine tanks require plenty of dechlorinated water, but your goal is to replicate the wide variety of chemicals in the quantities found in natural sea water. It involves replenishing the trace elements extracted by using a reverse osmosis (RO) unit or any other method employed for removing the toxins in tap water, that also takes out many of the trace elements needed for the well-being of the occupants of your marine tank.

Tank temperature

Red sea coral reefWhile your freshwater tropical tank might have required relatively high temperatures, it could be that your large marine tank needs the opposite. While sea water can feel warm in the shallows when you go for a dip on holiday, the temperature can sometimes take a surprising nose-dive at the depths where coral may be found.

It may even be necessary to deploy an aquarium chiller to maintain the right temperature in your marine aquarium. Failure to do so can result in your fish suffering, as well as affecting your tank's pH levels, and it can lead to unwanted algal growth too. In larger tanks that employ significant amounts of T8 and even T5 lighting, this becomes especially significant as heat is given off as a by-product from your lighting rig, especially when using older and less efficient models of fluorescent lighting.

Another way to keep things a little cooler is to utilise the recent advances in LED aquarium lighting. These units are far more energy efficient and will give you the same lighting results with less heat output, although an aquarium chiller may still be needed to keep things running at an optimum level, especially on larger tanks.

Filtration, live rock and sand

A big difference in most marine tanks, as opposed to the majority of tropical freshwater aquaria, is that the environment in your tank is less inert. As in freshwater tanks with plenty of natural plants, your marine tank can benefit from live rock and substrates that are home to a range of sea creatures, helping your tank reach an equilibrium.

Sea anemonesThese living but largely unseen aspects of your aquarium form part of the nitrogen cycle, and so act as part of your tank’s filtration system, adding not only aesthetic benefit, as can be seen from these sea anemones, but practical functionality too, helping you to replicate a true coral reef in miniature.

Be careful though, because although most live sands and rocks are clear of nasties, those taken straight from the sea may contain parasites and unwanted creatures like tube worms, which grow quickly and can take over your tank, as they anchor themselves in place and envelops their bodies in tubes.

The final word

If you decide to keep a marine aquarium, be prepared as it is going to take patience, care and attention. Passion helps too – make sure this is something that you really want to do, and you’ll find the extra work in establishing your tank worthwhile, with the rewards being all the greater!