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Converting to a Marine Aquarium

There’s no denying that ornamental marine fish are beautiful.  If you’re local aquatic retailer has a display tank full of marine fish, inverts, flora and fauna, you’ll no doubt have been mesmerised by the mini eco system on display.

If you’ve kept freshwater fish for many years, making the leap to a marine system can often be quite daunting, with the additional equipment, the expense associated with the live stock and the demanding water quality conditions that need to be provided. This article is designed to outline how to make this leap into the marine world – explaining everything you need to know when swapping from a freshwater fish tank to a marine system that includes easy to keep marine inverts. When I say easy to keep, I’m referring to the more hardy soft corals that are available such as Leather Corals and Button Corals, rather than Hard Corals and anemones which can be a lot more involved. We’ll do this by converting a Juwel Vision 180 from a freshwater set up to a marine invert set up – and we’ll assume that the fish tank is empty to start with!

Equipment List:

We’re assuming the starting point is a standard Juwel Vision 180, which includes an integrated filter, heater and T5 lighting system. In addition to this equipment you’ll require:

  • Juwel 3.0 Protein Skimmer
  • 2 x Circulation Pumps
  • New Filter Media, including Fine White Pads, 2 x Coarse Blue Pads, Phosphate Removing Pads and Activated Carbon such as Fluval Lab Series Activated Carbon which includes a media bag
  • 1 x T5 Marine White Fluorescent Tube
  • 1 x T5 Marine Blue Fluorescent Tube
  • 2 x Juwel Reflectors
  • Marine Reef Salt (buy a bucket to get the best value for money)
  • Hydrometer
  • Waterlife Biomature
  • Test Kits - you’ll need to test Ammonia, Nitrite and Nitrate as a minimum
  • 1 x Box of Live Rock
  • 1 x Bag of Substrate

Optional Extras:

  • If you have a reverse osmosis (RO) system, or can purchase RO water from your local aquatic retailer then that’s a great addition and will start you off on the right track – with totally pure water. If not, it’s not the end of the world, just make sure you measure your tapwater’s nitrate and phosphate levels. If you get a reading and you don’t use RO water, you’ll likely have water quality issues in the long term.
  • Water Butt, spare (low wattage) heater and small circulation pump or air pump with airstone. If you’ve space in your garage, mix your saltwater in large quantities in the water butt. It’ll make life so much easier in the long run as you’ll have fresh salt water available for regular water changes.

Step 1 – Adding the Equipment

Adding The Equipment

Most of the new equipment can be added to the Juwel Vision 180 at this first stage, before adding any water. The lighting system should be unplugged from the mains, with the two new Fluorescent bulbs being added. Check the end caps if you’ve had the light unit for some time as these may need to be replaced at the same time. Personally I prefer to place the blue bulb at the front of the aquarium with the white closer to the back as this will help to bring out the colours of your fish, as well as the inverts.

It is important to use a mixture of blue and white bulbs if you’re looking to house corals, as this helps to replicate the natural light conditions in tropical areas, taking into consideration the depth of the water where the corals will naturally live. Don’t forget that the great majority of corals depend upon photosynthesis to prosper, and that over time Fluorescent Tubes will fade. With this in mind you should replace them every 6 – 12 months to ensure you’re providing the optimum lighting conditions for your livestock.

At this point I also want to note that two T5 Fluorescent tubes should be seen as the minimum used. If you can increase the number of T5 tubes in the hood, or are able to fit LED lights in addition to the standard Juwel lighting, this will allow you to keep more sensitive and light dependent inverts within the aquarium. If you’re keeping leather and button corals however, two T5 tubes should be fine.

Once you’ve installed the two fluorescent tubes, add the reflectors to ensure that the light generated is directed into the aquarium.

Now that the lighting has been updated, the Juwel Protein Skimmer can be added into the back left corner of the aquarium. This type of protein skimmer is highly recommended for all Juwel Aquariums and is a very welcome addition to their product range. For many years we had to attack our Juwel Aquarium hoods with a hacksaw in order to fit a protein skimmer – which was never ideal!

The Juwel Protein Skimmer 3.0 is secured within the aquarium by a bracket that needs to be siliconed to the side of the aquarium - please note this will take 48hrs to dry and the glass needs to be dry before attaching. New versions of the Vision 180 will be delivered with a cut out in the top of the rear access panel of the hood, through which the protein skimmers cup can protrude. If you have an older Vision 180, replacement flap sets are available, alternatively you can cut a hole yourself.

The great thing about this skimmer is that it can be installed nicely, with the lid of the aquarium shutting properly. This will help prevent your fish from leaping out of the aquarium if spooked, and will stop your living room being flooded by light from the back of your fish tank!


Now that you have your lighting and your protein skimmer in place you can ensure that your aquarium heater and Juwel filter is clean and ready for operation. Media wise, ensure you’re using fresh media that has been rinsed prior to putting into the standard Juwel filter.  Unlike on freshwater applications where the internal filter is used for biological filtration, we don’t want to encourage this in a marine set up. It is for this reason, we’re not using Juwel Cirax in the filter. Instead we’re using a coarse blue and fine white filter pad purely for mechanical filtration, and a high quality activated carbon filter media and phosphate sponge to keep your water crystal clear whilst removing any contaminants that may find their way into your water. Layer the media with the coarse foam at the bottom, the carbon and phosphate sponge in the middle, the fine white filter pads, and a coarse layer at the top. This should prevent your chemical media from clogging, and will reduce the number of times you’ll need to replace the fine white pads.

A note on biological filtration: in a freshwater aquarium, the bigger the filter the better, and biological media is a great addition. In a sensitive marine environment however, if you use a large external filter or place biological filter media within your Juwel filter, you’ll find that your levels of nitrates will quickly rise which is not a good situation to be in if you’re keeping any inverts (as we intend to do). So keep them out of the aquarium! Instead, on this set up we’re going to use the high powered protein skimmer, and the live rock to provide the filtration.  The integrated Juwel filter will only be used for mechanical and chemical filtration, and as a handy place for the heater, nothing more.

The final thing to do in this step is add the substrate. Assuming your’re using coral sand, simply rinse well before adding to the aquarium (it won’t be well enough but it will help a little!). If using a ‘live’ substrate, don’t add this until the end of Step 2.

Step 2 – Adding the Water

Now that you’ve the majority of the equipment is in place, it’s time to add your water. Ideally if you have access to RO water, use this to ensure you’re not adding any pollutants on day one. If not, and you have no nitrate or phosphate readings when testing your tap water, it’s time fill the aquarium.

Keep the water level a few centimetres below the max fill level, as when you add the salt the water level will increase. Once filled, add a dose of dechlorinator and then switch on your heater and Juwel Filter which will start to warm and circulate the aquarium’s water. This will also help trap the sediment from the coral sand which will inevitably be clouding the fish tank!

Note: Don’t switch the Protein Skimmer on yet, we leave this switched off until the aquarium has fully matured.

Step 3 – Mixing the Salt Water

It’s now time to mix your first batch of seawater, which really isn’t that difficult! Over time you’ll get the hang of this, although to this day I always add more salt than I should and have to dilute the mix down again!

Red Sea Coral Pro

As a guide, 25Kg of salt will mix approximately 600lts of saltwater. So for a 180lt aquarium, you’ll need approximately 7.5Kgs of salt – and when you’re mixing it for the first time it’ll seem amazing that so much salt is needed! Unlike me, try to add less salt than needed, so you can gradually add more to achieve the correct salinity – if not you’ll have to waste some of the water you’ve mixed, adding fresh water to lower the salinity to the correct level.

Once you’ve added what you think is the correct quantity of salt, allow it to mix for several hours, helped by the Juwel filter pump and whilst the water comes to temperature.

Note: the salinity of sea water changes with temperature, so keep this in mind when mixing salt. Always mix it in water that is heated to the same temperature as your aquarium (which brings us back to the water butt being a great investment!).

Ocean Hydrometer

Now that you’ve waited a few hours (I’d recommend over night) it’s time to test the salinity of your water (assuming the tank is up to temperature). To do this we’ll use the Hydrometer as can be found in our Test Kit Section. Most will include instructions which generally include rinsing the hydrometer in freshwater prior to use. Once done, fill the hydrometer with aquarium water. The needle within the hydrometer will then move to inform you of the salinity of the sample. Keep an eye out for any bubbles that may be stuck to the needle, as this will give you a false reading. Your target salinity should be around 1.025.

If you find the water mixed is below this level, just add more salt. If you’re over (my approach), add more freshwater – until you reach the correct level. Don’t forget it may take an hour or so for the salt to be absorbed into the water, so this can take a while.

Step 4 – Maturing the System

This step may sound a little strange, particularly when I’ve already stated that we’re using Live Rock and a Protein Skimmer for filtration! Personally I think this is a sensible step, but others may disagree (comments are always welcome J).


Here’s why I’m taking this approach. When we add the live rock to the aquarium, it will be covered with flora and fauna that will have already been stressed by it’s extended journey as it made its way to our home, and it is likely that the beneficial bacteria that lives within the live rock will have been damaged. Adding it to a sterile aquarium that hasn’t been matured will inevitably cause additional damage, as Ammonia and Nitrite levels spike due to the decaying matter in the live rock. As such, I’d recommend that the aquarium’s water be matured prior to adding the live rock, as the beneficial bacteria that will have been added prior to the live rock will help to minimise any spikes in ammonia resulting from the addition of dead organisms within the live rock.

Salt Water Master

Waterlife Biomature is a great product for this with clear instruction for the process. In overview, you add the specified dosage of Biomature into the aquarium each day, and you monitor the levels of ammonia and nitrite. You’ll notice that after a few days the ammonia level will increase, before it then starts to fall again. The reason it is falling is due to beneficial bacteria consuming the ammonia. At the same time the ammonia levels decrease, the nitrite will increase. This is because the bacteria that consume the ammonia produce nitrite as a by product. The next colony of beneficial bacteria that arrives will consume the nitrite. Again you’ll know when they’ve arrived as the nitrite level will subside. You should only add your live rock once both ammonia and nitrite levels are zero, which may take a few weeks.

Step 5 – Adding the Live Rock

Live Rock

Now that the fish tank has matured, it’s time to add the live rock. This will generally arrive in plastic bags, but not immersed in water. Take the rock pieces out of the bags and inspect them thoroughly, keeping an eye out for small crabs. If you spot any, don’t add them to the aquarium – they will be a nightmare to get rid of and will likely cause havoc! If you’re confident you have no unwanted hitchhikers, add the rock to the system, removing water as required to stop the aquarium from overflowing!

When aquascaping, you may notice that the rock pieces may have algae on one side but not the other. Try to ensure that any surface that has anything living on the surface is positioned to face the aquarium’s lights, encouraging growth. This is one of the great things with live rock, you’ll have a fantastic eco system will all sorts of creatures in no time at all.

You may have noticed that I’ve not yet mentioned adding the circulation pumps. Now is a great time to do this, hiding them as well as possible within the live rock, whilst ensuring you’re still able to access them for maintenance.

If you’re swapping from a freshwater set up to a marine and invert setup, water circulation is the next most noticeable difference, as you upgrade from a sedate backwater to the raging torrent of the ocean! As a guide, you’ll want to circulate atleast ten times the volume of the fish tank every hour, that atleast 1,800lph on our Vision aquarium. Personally however I like to add a little more, so I’ll be adding two Hydor Koralia Evo 4000s with a total output of 8000lph, one at each end of the fish tank! When used in conjunction with a wave controller, this will provide fantastic circulation within the aquarium, minimising the likelihood of dead spots and keeping my fish entertained.

Step 6 – Nearly There


Well, now that you have the aquarium set up, the water matured, the live rock in place and the circulation pumps generating plenty of current, it’s time to switch on the Protein Skimmer!

Protein Skimmers are a great invention and no marine tank should be without one. Newer models such as the Juwel 3.0 Protein skimmer use a pump with a venturi fitted. This creates vast quantities of air bubbles within the confined space of the skimmer. Organic waste products are attracted to the bubbles which slowly rise to the water’s surface. This creates a foam which rises into the collection cup of the skimmer, from where it can be easily disposed of.

An efficient protein skimmer will remove 90% of the organic waste from a marine aquarium – which is why you definitely need this piece of equipment.

The protein skimmer will help to remove any pollutants associated with the introduction of the Live Rock, however it is important that you continue to monitor your ammonia and nitrite levels. After a week, if you’ve had no increases, it’s time to think about introducing live stock.

It’s also time to switch on the lights if you haven’t already. Ideally you’re lighting should be switched on for 8 to 10 hours per day, and just as importantly, it needs to be switched on for the same 8 to 10 hours each day. With this in mind, I recommend you use an electric timer to switch the lights on the same time each day. You can set this so that the aquarium’s lights are switched on during the evenings when you’re most likely wanting available to view it (not being stuck at work).

Step 7 – Adding Livestock

If you’ve kept tropical fish, you will already be accustomed to the acclimatisation process. With marine fish and inverts there’s just one added element to take into consideration, the salinity.

When introducing livestock, including coral, shrimps, fish etc., we recommend the following process:

  1. Switch off the aquarium lights
  2. Gently transfer the livestock and the water  from the transportation bag into a container (sandwich boxes are great) which can then float in the fish tank
  3. Leave the box floating whilst the water within the container adjusts to that of the fish tank, you can use a thermometer to check
  4. Start to introduce new water from the fish tank, in small quantities, into the container – allowing your tank’s water to mix with the transportation water. If the container has too much water, remove some, but NOT by pouring it into your fish tank! (I’ll explain why afterwards)
  5. Continue to change the water slowly in the container, until it matches the salinity of the aquarium
  6. Gently release your new livestock into it’s home

This process may take several hours, patience is however well rewarded. It’s especially important that you do not expose your livestock to sudden changes in salinity (specific gravity). Inverts such as shrimps or corals are particularly sensitive to these changes.

Note: I mentioned in point 4 that you should not pour the water from the transportation bag into your aquarium, and there’ a very good reason for this. If you’re adding a new marine fish that has been housed in a fish only system at the aquatic retailer, you can’t be sure that they haven’t added any medications into the system that are copper based. Copper is toxic to all inverts. As such the last thing you ever want to do is mix water from an aquarium shop’s marine system that may be medicated into your invert tank! It’s always best to stay on the side of caution, don’t add any water from your local fish shop’s system, stick to your own.