Fish Only Or Reef?


Once the initial interest in owning a marine aquarium has been aroused the natural continuation is what type to have. Some potential aquarists will not realise that there is a choice and this is understandable. When the thought ‘marine aquarium’ arises the reef appears, as seen on television and maybe in reality. Many dealers also display a reef system.

There are choices though, three of them. Two are common, one not so. First is the fish only system, then the corals only reef, then the mixed reef. There are few coral only systems as there are few aquarists who can resist having fish.

The very important thing for a new aquarist to consider is the potential for trouble with these systems. That sounds very negative but the danger factors, inexperience and lack of patience, should be taken into account.

Walking into a marine store the potential aquarist is confronted by beautiful fish and corals and as mentioned earlier often a beautiful mixed reef aquarium. It is perfectly understandable for the powerful magnet to begin to work, giving the visitor a vision of a similar system at home.

The best reaction is to have a look round, ask any questions that come to mind, then leave! Not so easy but necessary.

Leaving the store has activated the first requirement of a successful marine aquarist – patience! If the storekeeper is a good one, the different systems that are available may have been mentioned.

When home the first consideration is ‘where and what size’. Placement is important bearing in mind that a full aquarium is very heavy – it needs proper support. There also needs to be adequate access to the back and sides of the system for maintenance purposes. Now that this has been decided consideration of the type of aquarium can be given.

Fish only does not mean an aquarium with just some fish in, though of course this is the basic idea. Fish only systems can be very attractive with different coloured and shaped fish swimming above a ‘reef’. The reef does not have any corals, it is a number of carefully arranged rocks. These rocks will, in time, change colour and add significantly to the aquarium picture. Importantly, the rocks will give the fish a place to hide when night arrives making them feel secure and not stressed. A fish only system can hold many more fish than a mixed reef, roughly perhaps twice as many (fish load is calculated using the aquarium net gallonage and the length of fish excluding the tail, so if they will grow into larger fish then there will obviously be less of them).

Are there any advantages with a fish only system? Particularly for a beginner there are. With seawater quality being the number one requirement in a marine aquarium there is a real advantage as generally fish are less sensitive to reducing seawater quality than corals and if the beginner has selected fish carefully they should tolerate the mistakes, such as over feeding, that are likely to occur. Also, should the aquarist be unfortunately faced with disease then because there aren’t any corals medications that are effective and easily obtained can be used. Lighting is more simple, with colour enhancing fluorescent tubes being sufficient, basically the need is to see the fish and let the fish see.

A corals only reef system is not often seen as said. However, there is one massive advantage to these systems and that is the lack of fish. Again as said, seawater quality is the number one requirement and as there aren’t any fish and thus there isn’t any fish food being used then the potential pollution of the seawater is greatly reduced. This doesn’t remove the requirement for maintenance of course which includes partial routine seawater changes but it does make life easier. However there aren’t many aquarists who would choose this type of system because it doesn’t give quite such a lovely picture as a mixed reef. Ok, fair enough.

The mixed reef, corals and fish, is the most difficult system to maintain successfully. This is not so much because it is technically difficult because of complexity, but more because of the higher quality requirements that are needed and the more likely that a beginner’s mistakes will have more impact. Generally corals require constant high seawater quality. Every day the new aquarist is feeding the fish and this food goes through the fishes system. That which doesn’t and sinks into the rocks will rot down. Fish waste and rotted food means reduced seawater quality which will in a fairly short period have an effect on the corals. Definitely not wanted! Also, most corals require high quality lighting. A couple of fluorescents will not do. At least there will be a bank of specialized fluorescents. With some corals there will be the need for more high powered lighting and this of course means the mixed reef is a larger financial investment (which it is anyway, the higher powered lighting adds to it). The aquarist could decide that soft corals will be used as these are generally hardier than the hard coral types and require less light, this is so but it  doesn’t apply to all.

So there it is, two main choices. Once the choice is made and the fact that patience is required has been accepted another word that is essential for success needs to be introduced, and this word is research. A fish or coral should never be bought because it looks so lovely, that is, bought on impulse. It should be researched so that the necessary requirements such as habitat and feeding are known plus any lighting needs. Also, how big will it eventually get?

Once the type of system has been chosen there is more to do. It’s patience and research again! Find out what equipment is needed and how much it will cost. How much will the livestock cost? How much will the system cost to run?

All of this patience and research is a pain, there isn’t any doubt about it, but by doing the necessary and controlling the impulse to just ‘get it’ the chance of success is increased massively. Once the research is complete the aquarist has the confidence to go ahead as it is known that the initial cost of the system and the future running costs can be afforded. The aquarist also knows the needs of the livestock and will be prepared for their proper husbandry. It could be said that failure to carry out basic research is cruel to future livestock.

This talk of patience, research and system choices could put some off, and if that is the case I’m glad it does. If the hopeful aquarist is not put off, then this indicates a reasonable attitude from the start and there is every chance of success. Information is available from many sources on the web. This site has a huge amount of information as can be seen by clicking on ‘Categories’ (top of page) or the site map, there’s also a search facility.

Keeping a marine aquarium and the initial research is not difficult. Once the ‘itchy’ period (I like to call it that as there is an itch to just get on with it) is over then for many years the aquarist should be repaid by a beautiful, educational and fascinating hobby.


  1. Hi there to every one, the contents present at this site are truly awesome
    for people knowledge, well, keep up the good work fellows.

  2. I’m still learning from you but I’m making my way up as well. I certainly enjoy reading everything that is written on your blog. Keep it coming. I enjoyed it!

  3. Hello db. Glad you’re finding aquaristsonline useful!

  4. I believe if you are really interested in getting a saltwater tank and you have read up on it and still plan to move forward you may be in enough that you will end up wanting live corals. If there is a chance you may want a reef tank then you should always have reef safe fish so you do not have to give up animals or start a second tank.

    Many “soft corals” can be hardier then fish and tolerate more significant swings in chemistry. I use quotes around soft corals as some scientist would say these animals are not true corals, but they are beautiful and great for new aquarist. When we are starting a new system we often add Zoanthids, Protopalythoa, and corallimorphs(“mushrooms”) a week or so before adding any fish. If the temp drops, salinity gets high, or oxygen levels are depleted fish die quickly which the soft corals mentioned above will just close up for a while and make a full recovery if conditions are restored quickly.

  5. Thanks for the info, very welcome.

  6. I believe it’ s better to start with a reef only aquarium and after a bit of time, once you’ve learned a bit more from your 1st installation, then start a mixed one.

  7. Hello. I take it you mean a reef aquarium with only corals and add fish later. This I agree with as it gives the corals a chance to attach and settle and the aquarist time to adjust rocks and coral positions before fish appear, this will reduce fish stress and be positive towards a healthy aquarium. I started my current aquarium 10 years ago in September and fish went in April the next year. Perhaps a long wait like that isn’t absolutely necessary but there hasn’t been any problem with the system or inhabitants at all (I did lose a fish, a damsel, but I believe this was an age thing). A lot different from my very first mixed reef 40 years or so ago!

  8. Hello K&K glad you find the site good.

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