Converting A Tropical Aquarium To A Marine Fish Tank

Many people with tropical fish tanks think about making the switch to a marine aquarium set-up at some point, but often change their minds when they think about having to invest in a brand new fish tank and fish tank equipment. Let us reassure you, a lot of the products you use with your freshwater fish tank are also suitable for saltwater fishkeeping! If you follow the below checks and tips, you will be ready to make the transition to a fantastic new marine fish tank.

What Type Of Fish Tank Do I Need?

The freshwater fish tank you currently have should be perfectly fine for supporting marine life – almost all fish tanks are suitable for any type of water. With that being said, look out for the following features in your tank that would not be good in saltwater:

  • Exposed metal screws. If saltwater will be constantly splashed over metal screws they will corrode after a while.

  • Check that the light fittings in the hood are waterproof. If they are not, this means that saltwater will creep its way into the fluorescent light tubes and ruin them.

  • One thing that is easily overlooked is the silicone found at the edges of most aquariums. Some water treatments and fish medications have doses of copper in them which can become (sucked into) the fish tank silicone. When you fill the aquarium up again with saltwater, this copper can come out and is toxic to marine coral. So, if you notice that the silicone in your fish tank is discoloured (a blueish/greenish colour) it is best not to add coral to your marine set-up.

Always remember to wash over the aquarium glass thoroughly before filling your fish tank again. It is best to use RO water when doing this.  

Clown Fish

Saltwater Tank Gravel / Substrate

The preferred substrate in marine tanks is sand or crushed coral. This is what most saltwater livestock prefer and will benefit from. Sand will assist with keeping alkalinity levels high, which is what your water will need. If you use sand in your freshwater tank, then you are good to go. If you currently have gravel, it is probably a good idea to get some aquarium sand.

  • Tip: Live sand will help to kickstart the water filtration process.

Marine Fish Tank Filter / Filtration

It is highly likely your current filtration system is suitable for saltwater fishkeeping (this excludes under gravel filtration though - this will clog up far too quickly). If you have an external filter like the top-selling EF1 or our new and improved EF+1, these can easily be used in a saltwater setup. Be aware that marine fish tanks require more filtration than freshwater, so make sure the external filtration you currently have is large enough.

If you prefer an internal filtration system, All Pond Solutions sells a variety of internal, corner and hand on filters for smaller aquariums. These compact internal filters provide both mechanical and biological filtration without taking up space outside of your aquarium.


The lights that you have on your current freshwater aquarium will be suitable during the early stages of your marine tank. Though, to enhance the colour in your marine fish and to ensure that your coral survives, actinic (blue) marine lights with higher kelvin will be necessary.

Marine Fish Tank

Pumps / Powerheads

Tropical tanks do not always need the same water flow that marine tank requires. The surge of water created by a pump/wavemaker to create waves in your water is important when keeping marine fish. If you do have a water pump currently, it will run just fine in saltwater. We advise opening up the unit and checking the shaft – ensure that this made from a material that will not rust.                           


Almost all aquarium heaters are compatible with freshwater as well as saltwater. While we recommend that you check the specifications on your current heater, it is likely that you will not need to replace this piece of equipment when switching fish tank water set-ups.                   


If you have artificial rocks, artificial coral or stones in your freshwater tank, and wish to keep them, these will be perfectly suitable to have in a marine fish tank. It must be advised that plastic aquarium plants should not be kept - there is a good chance that marine fish will nibble on these and the plastic will be extremely dangerous to your fish and their digestive tracts.

       Salt Water Fish      

Testing Your Water 

The water tests that you have for your freshwater tank will not be suitable for a marine fish tank. The water parameters that need to be measured in a saltwater aquarium are completely different and very important to keep track of. We have a selection of marine treatments and test kits that are great for tanks with fish as well as coral.
You will also need to make sure you have a supply of sea salt, a hydrometer and dry or frozen food that is marine appropriate when you have a saltwater fish tank.

You can find all glass tanks and fish tanks designed for a marine aquarium on our website, in addition to testing kits, subrate and all of the equipment needed for the perfect saltwater tank!