In a [tag-tec]saltwater aquarium[/tag-tec] it is preferential to have both nitrates and phosphate as well as various other nutrients at the lowest possible level you can achieve.
Growing algae in the sump or in the refugium is an excellent way to remove nutrients from the water column, good examples which are nitrate and phosphate.
Once established the algae in the sump/refugium can reduce the nutrients to a very low level.
So why would you want to harvest this algae when you have spent all this time trying to make it grow?
What happens is that the algae in the algae bed, dependant upon the species being grown will grow in line with the water movement which passes through the bed. Over time the algae will form quite a dense ‘forest’ of algae – so much to the extent that a lot of the light provided will not be able to penetrate through to the lower levels.
Now you may think that this is ok as the leaves at the top will be able to grow using the light provided, however what happens is that the leaves and/or plants lower down in the sump/refugium will actually die.
When most algae die the nutrients which have been processed are released back into the water column, therefore all those nutrients which have been removed are suddenly released back into the aquarium water.
There are times when the entire algae bed dies and all the nutrients are instantly released back into the aquarium. When this happens your system will be loaded with nutrients and various problems can occur.
Therefore when you grow macro algae in your [tag-ice]sump[/tag-ice] or [tag-tec]refugium[/tag-tec] it is imperative that from time to time you harvest it.
Basically harvesting the macro algae means thinning it out.
To harvest the algae simply remove some of the algae, but do not remove any of the roots as this will prevent it from growing back. I personally use an old pair of scissors and give the algae bed a haircut!
When you harvest the algae what you are doing is removing a lot of nutrient laden plant life from the water and exposing what remains to the light provided to them. The macro algae will then start to re-grow removing even from nutrients from the water column.
Over time the algae bed will re-grow and eventually it will be time to harvest it again.
It has been noted by numerous aquarists that harvesting the algae bed the number of algae bed crashes experienced has significantly reduced.
When you remove the algae do not be tempted to feed it to the aquarium inhabitants as you are effectively feeding nutrients back into the water. Either throw it away or give it away to another aquarist who is just starting a new algae bed.