Caring for your ferns in your aquarium.

Most aquatic plants are happiest with soft, slightly acidic water. A major factor is that the plants will have more available CO2 in these conditions. Investing in a CO2 injection system will make a noticeable benefit to aquarium plants. There are also ‘liquid carbon’ additives available now that claim to make carbon more available to plants, if CO2 injection is not possible. The theory is that when the molecule breaks down it releases carbon dioxide into the water. The science is flaky, and the amount of carbon released seems unlikely to make much difference. 
 

Most tap water is not soft. In an ideal world you may want to consider a water softening system, either a two-column water deionizer or a reverse osmosis system. Standard domestic ion exchange water softeners are not suitable due to excess sodium chloride. Pure water will need to be ‘remineralised’ before being used in an aquarium. All this water preparation is very time consuming and needs an advanced level of commitment. Some aquarium shops will sell deionised water specifically prepared for their customers. Rainwater can be used, but if you are also keeping fish there is a small a risk of introducing disease, parasites and polluting chemicals. However, this is less of an issue if you are just maintaining an aquarium to keep ferns.
 

The water temperature needs to be maintained around 25 °C using an aquarium heater. Lower temperatures can work for many aquatic ferns although growth will be slower. A water filter is recommended, although not essential, to help circulate the water. Pumping air into an aquarium is not recommended, although it is a good way to circulate the water, it will drive out carbon dioxide which is required for good plant growth. Undergravel filters will interfere with root growth, so should not be used if you intend to grow plants. Small regular water changes are also recommended to reduce the general build-up of salts, like nitrates, over time. For the serious aquarist, test kits are available to monitor many factors of your water chemistry.
 

There are many substrates on the market, available in many colours. Modern aquarium gravels designed for plant growth tend to be finer, approaching the consistency of sand. Normally they are made from inert materials, either natural rocks, usually silica sands, or man made products. If you are growing aquatic epiphytes and lithophytes you only need a very shallow depth of substrate and this is primarily for aesthetics. Newer ‘aquasoils’ are available which resemble fine gravel but are actually small balls of mineral rich volcanic ash soil that is then baked. Their composition will help to slightly lower and stabilise the pH of the water which is beneficial to most aquatic plants.
 

Aquarium plants will need fertilising. General aquarium plant fertilisers differ from regular NPK fertilisers and should contain a balance of nutrients for the needs of your plants. Over-fertilising will encourage algae growth.