At What Times Should The Lighting Be On Above The Refugium

In the refugium we are attempting to grow macro algae. The reason for this is that as they grow they remove nutrients like nitrate and phosphate out of the water.

In a previous post I have discussed what type of lighting should be used so that you can get optimum algae growth plus I have also talked briefly about harvesting the algae from time to time.

One thing which I have not really touched upon is how long you should provide lighting for.

There are two methods available – one which I agree with and one which I don’t.

I shall cover the one that I don’t agree with first.

Option 1 – Provide Lighting Over a 24 Hour Period.

So why don’t I agree with this?

Basically it’s because it does not happen in nature. There are some aquarists who believe that providing lighting over a 24 hour period prevents algae crashes from happening. This is where all the algae suddenly dies and all the nutrients which are removed are released back into the aquarium.

To me this has never been proven. If you look at nature the algae beds in the sea are exposed to sunlight over a determined length of time. The same as provided for the corals. You would not leave your lights on for 24 hours to provide light for the corals so why do it for the algae.

I am firmly of the opinion that we should attempt to replicate nature wherever we can. It works in nature so why try to change it in our aquariums?

I also believe that the algae needs a rest!

There is another factor to this as well. This is that in darkness the micro organisms come out more and start to feed and reproduce. It has been noted by many aquarists that they have experienced a pod explosion when the lights are out for a length of time.

Option 2 – Provide Lighting Over A Shorter Period.

This is my preferred option.

I have covered some of the reasons above. i.e. lighting is not provided over a 24 hour period in nature so why do it in our aquariums and the factor of the little critters which we are providing refuge to.

So how long is a shorter period. Well it can be many things but the method I use is that the lights above the refugium turn on when the main lighting turns off above the display aquarium – i.e. the metal halide lighting. They stay on all night and turn off when the metal halides turn on the next day. This is sometimes called reverse sunlight lighting.

So why do I do it this way and not have them on at the same time as the metal halides?

Basically this is so that I do not experience a drop in pH over the nightime hours. The reason this happens is that when the lights are on photosynthesis occurs, carbon dioxide is used and oxygen given off into the aquarium and the pH rises or in this case remains stable.

Stability as we all know is a major factor we are all hoping to achieve.

If we had the refugium lights on at the same time as the main display aquarium when all the lights went off there is a possibility that the pH will drop.

So that’s why I prefer option 2 – it simply makes sense to me.

Another thing that I also do is occasionally turn off the lighting above the refugium for a couple of days. I have found that when I do this I get a lot more ‘critters’ in the refugium. The more ‘critters’ there are the happier I am!


At What Times Should The Lighting Be On Above The Refugium
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