Ifyou already have a freshwateraquarium, but fancy trying yourhand at saltwater, you may bewondering whether to convert your

existing set-up to marine. It's a commonquestion and in fact it can be surprisinglyeasy to establish a successful salty systemin this way.

What are you going to keep?Firstly, it's worth planning out the type ofsystem you'd like to achieve, along with awish list of potential livestock. There arethree main approaches to consider:

Fish-only: As the name suggests, this typeof system centres purely on marine fish,with no invertebrate stock. This is a classicset-up for fish such as morays, large lionfish,large puffers and aggressive triggers, butsmaller, peaceful species can also obviouslybe maintained in this way. Biologicalfiltration tends to be based on traditionalmethods widely used in freshwaterfishkeeping (such as canister or tricklefilters). This represents the moststraightforward system for conversion froman existing freshwater aquarium, withminimal additional equipment (notably aprotein skimmer) often being necessary.

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Fish only with live rock (FOWLR):This system also houses fish, but employslive rock to fulfil either part, or all, of therequired biological filtration, Far from beinga 'poor man's reef', this is all ideal set -up forfish which would otherwise munch coral,such as many angels and butterflies, but thesky's the limit as far as the fish you couldkeep. Again, this Callbe a fairly simple

conversion project, and FOWLR systemscan be nm with just a little additionalequipment. Think of this system as anintermediate approach between thefish-only and reef tank.Reef:A reef system houses invertebrates(including corals), usually alongwith fish.Although live rock and sand are exclusivelyused for the bulk of biological filtration,

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these systems are the most demanding interms of water quality, lighting and watermovement, and there may be significantadditional equipment needed. Even so, it'sperfectly possible to run a full mixed reefpartly using the components of a freshwatersystem; some substantial pimping will benecessary, but it can be done.It's possible for the system to evolve over

time, so it's worth considering this whenplanning. For example, a system could beinitially set up as a FOWLR aquarium, andas experience and funds permit, it could bedeveloped into a complete reef, withlivestock and equipment added gradually.

How important is live rock?Live rock comprises chunks of coral rubble,naturally broken from the reef, which hasbeen colonised with a range oflife forms.This includes bacteria responsible fornitrification and denitrification as well asprotozoans, crustaceans, worms, algae, anda host of other organisms which collectivelycycle and process waste. Properly cycled or'cured' live rock (where die-off duringshipping has been managed by the dealer) isexpensive, but it's an important componentof the FOWLR and reef aquarium. Ifsufficient live rock is available and

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bioloading isn't excessive, live rock can fulfilall the biological filtration needs oftheaquarium, and using additional filtrationcan simply lead to issues with nitrates. Areef system will ideally have lkg of live rockper 10 lj2.2 gal aquarium volume - so for a250 lj55 gal aquarium, reckon on 25kg oflive rock.

Re-using the tankAs long as it's watertight, pretty much anyglass or acrylic tank will be suitable for amarine conversion, so that's potentially abig chunk of the budget accounted for. Sometanks feature aluminium trims, and thesecould be a possible worry. However, if theyare not subject to any significant corrosion,these trims are unlikely to add significantamounts of metal to the water. The tankwill need a thorough stripdown and cleanbefore setting up. Using a non-abrasive pad,scrub the panes with white vinegar toremove any limescale build-up and rinsewell in clean water.

What about a sump?If your freshwater system already has asump, you're onto a winner, and you caninstall all your equipment there with noproblem. If not, consider whether to retrofita sump. Sumps aren't essential for a marineaquarium, but they increase system volume(always a bonus) as well as adding extraflexibility, allowing for unsightly equipmentto be safely stashed out of sight, improvingthe aesthetics of the system and facilitatingeasier maintenance. The more complicatedthe system's technical requirements, themore a sump will prove necessary toprevent the tank itself'becoming cluttered- but a fish-only or FOWLR tank can easilybe setup without a sump.There are two ways to incorporatea sump:Drilling the tank to include an overflow orweir. This takes a certain amount of skilland patience, and is best left to aprofessional- your local aquatic shop maybe able to help. Drilled tanks offer the safestand most reliable way of sending theaquarium's water down to a sump.Alternatively, an overflow box can be

employed. These use a syphon to draw

Marine

Don't skimp onthe skimmer!A key item of equipment for the marineaquarium that isn't found on freshwatersystems is the protein skimmer, and forthe best chance of success, you'll wantone regardless ofthe system. A decentskimmer represents a considerableoutlay of cash, but it's one of the bestinvestments you can make. Don't skimpon the skimmer, and research theavailable range of models thoroughly.There's a skimmer to suit most marine

conversions, with sump-based,'hang-on' and internal models beingavailable. If possible, opt for anoversized skimmer for maximumefficiency.Protein skimmers directly remove

dissolved organic compounds (DOes)and suspended particles, which lead topoor water quality, by passingaquarium water into a reaction chamberinto which a mist of fine bubbles isintroduced. Parts of these organicmolecules are hydrophobic ('waterhating'), and they become attracted tothe air bubble. As the bubbles rise inthe reaction chamber, the organicsform a foam which is pushed upand out of the skimmer into a collectioncup, whereby they are exported fromthe system.

water from the main aquarium to the sump.Set up and maintained correctly, overflowboxes can work well (providing the syphondoesn't break), and tins method allowsfor a sump to be installed without drillingthe tank,

Cover glasses and hoodThe trend in marine aquariums has beenvery much towards open-topped tanks.However, there's no reason why a hood froman existing freshwater system can't be used(especially if tins incorporates the lightingtubes; but it's important that the hood issufficientiyventilated to ensure adequategas exchange).Cover glasses can hamper gas exchange, so

these could be left out, although they can beused if fish prone to jumping are kept (suchas eels, various wrasses and firefish) -but you'll still need to ensure adequateventilation to achieve saturated,oxygen-rich water.

What about the filter?A fish-only system can utilise the samebasic filtration as a freshwater set-up. Aninternal power filter or external canister canbe used, and can fulfil the roles ofmechanical, biological and chemicalfiltration essentially in exactly the same way(although the bacteria responsible forbiological filtration are completely differentbetween freshwater and marine systems, sothe biological media will need to be maturedfrom scratch). Set up this way, fish-onlysystems have limited denitrification, sonitrates can build up, which will need to beremedied with water changes.FOWLR aquariums may augment the

biological filtration with a canister or tricklefilter, but this is only necessary ifbioloadingfrom the fish exceeds tile live rock'sfiltration capacity (for example ifIarge,messy angels are kept). Many FOWLRtanks simply use live rock to perform all thebiological filtration (which can achieve

Substrates and hardscapeEnsure aLLhardscapelf~8!!lmmaterials are suitable forl saltwater -live rock is a key

~:!t&:~f,tr'"feature of reef and FOWLRtanks, but fish-only aquariumscan use other materials,including dense ocean rock,lightertufa (although this canact as a nitrate and phosphate

,. 'sponge') and even imitation_~./'::..tl' resin rocks. Whichever-- material is used, make sure

it's not going to leach metals or othernasties into the water.Suitable substrates range from fine

aragonite sand, through coral sand orgravel to coarse rubble chunks. Thechoice of substrate will largely bedictated by the needs of the animals -many wrasse need a fine substrate fordigging and sleeping, for example,whereas burrowing shrimp can benefitfrom a mixture of particle sizes.

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natural denitrification, helping to keepnitrate levels low), but it's still possible toput a canister or power filter to good usehere. Load it with filter floss or foam andactivated carbon, and that's mechanical andchemical filtration sorted, plus someadditional flow.The reef system exclusively uses live rock

for biological filtration, and additionalbiological filtration isn't used, as it cancontribute to elevated nitrate andphosphate levels, which are bad news forcorals. As with the FOWLR set-up, acanister can still be utilised for mechanicaland chemical filtration on a reef, however.

Water movementWith the exception of, say, very fast-flowingriver biotopes, marine systems generallyneed more water movement than theirfreshwater counterparts (for a reef, you'relooking at a minimum oflOx turnover perhour, although 40x plus is now common formany reefs). This is to assist with biologicalfiltration (especially iflive rock is used), toprevent detritus settling in dead spots,ensure adequate oxygenation, and to assistsessile animals with feeding and riddingthemselves of waste, so it's likely you'll needto up the ante here. You can still use pumpsfrom a freshwater set-up, but double-checkparts such as impeller shafts are safe for usein saltwater. Ceramic and stainless steel arefine, but any pump with brass parts is adefinite no-no (this is a source of coppercontamination, which is lethal toinvertebrates). Brass tends only to be usedin pond pumps, but it's worth checking anyequipment before use.Additional pumps such as powerheads

will almost certainly be necessary,especially for reef systems that demandstrong water movement. Some pumps allowfor wave effects to be created, and these willbenefit all marine systems, from fish-onlyto reef.

Heating and coolingHeater/thermostats for use in freshwatershould be perfectly suited for use insaltwater, so there's no need to change these.Do bear in mind that reef systems inparticular are sensitive to increasedtemperature - temperatures nudging

30°Cj86°F stress corals and clams, causingthem to shed their algal symbionts(zooxanthellae) in a process known as'bleaching'. Therefore, if you're going to bekeeping invertebrates, it may be necessary toconsider chilling the aquarium in summer,either through the use offans (use thosespecifically designed for aquarium use) or byemploying a refrigerant-based aquariumchiller with a titanium heat exchanger.

Lighting it upThe aquarium's existing lighting is likely tobe geared towards maintaining plant growth(freshwater lighting tends towards a'daylight' colour temperature of 5000-6000K (K=Kelvin) which is towards tileyellow end of tile visible spectrum). Manymarine aquariums will need more intenselighting, so depending on the requirements ofthe marine set-up, the lighting may need tobe altered, augmented or swapped entirely.However, marine fish-only tanks can

technically be run using fluorescents suitablefor freshwater systems and such set-upsdon't demand high light intensity. Even so,many folks will opt to change tubes to acolour temperature oflO,OOOKor higher,which offers a bluer colour and a more'marine' aesthetic, Additionally, increasingthe number of tubes to encourage growth ofthe live rock's coralline algae will benefitFOWLRsystems.For a reef containing corals and oilier

light-demanding animals, a couple ofT8tubes just won't cutthe mustard. You'll needhigh output T5s, LEDs or metal halides (or acombination of these) with a colourtemperature oflOOOO-14000K, andadditional blue actinic lighting will make thecolours of corals pop.

Avoid using tapwaterYou'll still need to perform water changes.Regardless of the type of marine system,reverse osmosis (RO) water is best for saltmixes and topping off evaporation (and it'spretty much essential for reef systems), soyou'll either need to buy an RO unit if youdon't already have one, or buy RO fromyour dealer. Tapwater can contain nitratesand phosphate which you don't want inyour salt mix, not to mention heavy metalsand pesticides.

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