Planted Aquariums Part 1.

Planted aquariums require different management to that of a ‘normal’ tropical aquarium. The balance between providing a suitable environment for plants and one suitable for fish can be tricky.

Gas exchange      

Plants produce oxygen during day light through the process of photosynthesis and ‘use’ carbon dioxide. Fish require oxygen so during the day the fish are happy but during the night the oxygen level can fall dangerously low unless extra aeration is provided. Plants on the other hand require carbon dioxide; too much aeration can reduce the carbon dioxide in the tank and reduce the plant growth. Carbon dioxide is acid and oxygen is alkaline these can lead to pH swings during a 24 hour period and cause health problems in the fish. Therefore oxygen, carbon dioxide and pH all need to be monitored so that any adjustments can be made if problems occur. Automatic carbon dioxide dosing systems should reflect the daily changes in the plants and the fish’s requirement’s.


Hardness is a measure of dissolved salts within water. Most tropical plants prefer soft acid water. Soft acidic water has less buffering capacity and therefore the use of carbon dioxide dosing can greatly increase pH swings.


The substrate is not only used for anchorage but for a source of nutrients. Both gravel and sand that are commonly used in aquariums are nutrient poor and therefore does not allow for good root growth. They can however be used as a top layer over loam thus preventing mixing of this substrate with the water. Loam is cheap, readily available from aquatic centers (sold as pond soil) and contains slow release nutrients. Commercially available substrates contain slow release nutrients and are excellent substrates for plant growth.



Filtration requirements for the plants is pretty minimal, all the filter needs to do is keep the water clear of suspended soils and brake down some of the waste so that the plants can ‘use’ them for growth. Fish on the other hand require good filtration and gas exchange. As discussed before a planted aquarium needs to strike a balance between the needs of the plants and that of the fish. Use a filter over rated for the size of your aquarium so that it provides great water quality but use a spray bar return which gently ripples the surface. If you continue to get low oxygen levels during the night then add an air pump on a timer, adjust it so that comes on when the lowest oxygen levels occur. Try not to run the air pump all the time otherwise you will reduce the carbon dioxide which is vital for the plant growth. I always use carbon in the filtration as this reduces any discoloration of the water which would (if left untreated) reduce light penetration.


There are plenty of light systems available and these should be chosen so that they fit your requirements and the lighting needs of your plants. Different species of plants require different amounts of light therefore their placement under these lights are critical. Plants require around 10 hours of light. If algae becomes a problem split the lighting period. Algae grow best with 10 hours of continuing light whereas plants only require a total of 10.


A number of the fish I add to a planted aquarium are in there to do a job. Fish like the Otocinclus (otocinclus affinis) and the Gold Sucking Loach (gyrinocareheilus aymonieri) are ideal algae eaters, however they can get aggressive when larger. The Flying Fox (epalzeorhynchus kallopterus) is great for hair algae. Have a few Cory Catfish (corydoras paleatus) in there to turn the substrate. These Cory’s prevent algae build up on the substrate plus they also eat any food that hits the bottom. Pakistani Loach (botia lohachata) are great snail eaters. Snails always turn up in planted aquariums so it is best to keep them in check with a fish rather than using a treatment to kill the snails which can create more problems than they solve.

There are loads of other fish which do well in a planted aquarium. Just make sure that when you purchase them that they are suitable for your mix of fish and that they don’t eat plants!