Refugiums are becoming more and more popular nowadays as people are starting to realise the beneift that they can have upon the aquarium.
Refugiums, as the name states are a refuge for animals to live without fear of predation. It is also an area where macro algae can be grown to assist in the removal of nutrients from the water.
In a normal refugium macro algae is grown to assist in the removal of nitrate and phosphate. In the refugium may also be a scattering of sand, a deep sand bed or even a mud bed.
Macro algae normally will only remove nutrients when it is actively growing and for this to happen it requires a light source.
The best light source to use is lighting which is correct for the growth of plants – this is normally in the lower end of the kelvin scale.
In the display aquarium the lights are left on for between 8 and 12 hours however how long should the lights be left on above the refugium?
There are two answers to this question:
1. The lights are left on for a 24 hour period. With this method the algae is allowed to grow continuously and therefore remove more nutrients from the water column.
2. The lights are lit in what is termed reverse light cycle. What this means is that the lights above the refugium come on when the display aquarium lighting goes off and turn off when the display aquarium lighting comes on.
So what do I recommend and why?
Both options are valid options however I would recommend option 2.
The reason for this is that I like to follow nature. In nature the grass beds are not subject to lighting over a 24 hour period – the receive light when the sun is out!
I also believe that the algae needs a ‘rest’. It requires a lot of energy for the algae to grow and if it grows continuously then problems may occur. This is not something that has been scientifically proven but is something that I believe could happen. It also needs to be remembered that in the refugium other organisms also exist. There will be various types of organisms which, like most life would prefer a period of darkness. I read somewhere, unfortunately I cannot remember where, that in a refugium which was provided with darkness the population of organisms grew however if the lights were on continuously the population did not grow as fast.
There is another area which is important and both of the above methods provide this – pH stability. When the lights go out above the display aquarium there is normally a slight pH drop throughout the hours of darkness. If the refugium is lit throughout these hours of darkness then the pH drop may be countered. As with anything in this hobby stability is key and this is just another area where this stability can be maintained.
So in my opinion the refugium can be lit of a 24 hour period or it can be lit on a reverse cycle however if I was to choose then I would choose reverse cycle for the reasons listed above.