The move to more natural systems has helped to make a refugium an increasingly popular component for a reef set up.  As the name suggests it is primarily a part of the system that acts as a refuge.  In this case the refuge is for the smaller reef life.  A safe place to breed away from the predatory fish etc that would otherwise eat them.  It can be a sectioned off part of the main tank or a separate area like a sump.  If separate from the main tank they are usually well lit, and are often used for the growing of different types of Algae.

What is the function of a refugium ?

The intention, in my tank, is that it will fulfil a number of roles:

1.It should act as a breeding ground for the little critters that help feed the fish and corals.

2.Through the growing of Algae it will help to use up Phosphate and nitrates

In addition to this I have used a generic version of 'miracle mud'.  Why not miracle mud?  No reason other than the cost.  The advantage of using this type of deep substrate in the refugium is that it slowly dissolves, helping to replenish the trace elements and calcium levels.  Please note that you don't need to use a miracle (or generic brand) mud system as part of a refugium, sand will do.

Tell me how

There are many ideas for producing the 'best' functional refugium.   On my system, the sump acts as a refugium and as mentioned, uses a generic mud substrate.

Water flows into the sump over some bio-balls into the first chamber.  After this it passes through a bubble trap into the main section containing the mud substrate, Macro Algae and calcium reactor (Ca reactor is usually not used as part of a mud system).  Finally the water exits via a weir to be pumped back up to the display tank.

Click below for better quality image

 

 

Why have you mixed and matched?

With a normal stocking density of hard corals I probably would not have added a Calcium reactor.  After all, the mud substrate and deep sand bed in the display tank will provide a large amount of available calcium.  However, as we were always planning  on stocking with a high density of stony / hard corals it seemed prudent to add an extra and controllable source of calcium.  It was just as well, as the calcium use is now phenomenal, and would not be met otherwise.

What flow rates do I need for a separate refugium?

Most tanks use a weir system to return water from the main tank to the sump system.  The maximum flow rate is a function of the size (length) of weir(s) and diameter of the pipe(s) coming from them down to the sump.  To complicate matters, the number of bends is also important, as this will slow the water down.  Conversely with a sump based system, you should only get back down over the weir(s) what you have managed to pump up in the first place.  Therefore the flow rate of the return pump (up to the main tank) is also important, but must not exceed the capacity of the weirs to return it to the sump unless you fancy a salty swim.  In my system I have used two 1.5 inch pipes from my weirs which enables me to move just under 10,000 litres an hour.

The flow rate you choose (working within the constraints above) will depend on whether you are planning on using a mud filtration style refugium.  If not, the flow rate is not as critical.  I would advise that if you are planning on using a skimmer in the sump, it makes sense that the flow rate is at least equal to that of the skimmer.  If not, you may as well have purchased a smaller skimmer unit.  I would also suggest being able to cycle the entire volume of tank water at least twice an hour.

 Mud filtration systems on the other hand, do have specific flow requirements as well as recommended depths for the substrates.  This information is available from the respective manufacturers.  What follows is therefore just a guide, I would suggest checking the manufacturers web site for more detailed information.

How do I set the water level in the sump / refugium so it won't overflow if I have a power cut /pump failure

When designing a system it is a good idea to use one of the many sump volume calculators available on the net.  Using this, ensure the sump has sufficient capacity to take the volume of water, equal to about two centimetres of the main tank's depth.  This is in excess of the volume that you will require for the sump to have sufficient depth of water to function as a refugium.  When doing the calculations, bear in mind that you won't want the water lapping at the brim of the sump when it is in use.

Having done this in the design stage, there is a simple method to prevent a possible overflow situation that could occur if the system was overfilled and you suffered a pump /power failure.

1. Fill  the top tank so it begins to flow over the weirs back into the sump.  Then add enough water to the sump for the return pump to function.

2. Turn the return pump on, adding a little more water to allow the pump to function properly ( some water is used to fill the pipes).  After it has been running for a while, mark the level in the sump.

3. Check to make sure the return pump's pipe is not going to act as a siphon (The end in the main tank should not have its opening entirely beneath the water)

4. Turn off the return pump

5. After a short period of time the water will stop flowing over the weir(s), the pipes will drain and the level in the sump will stop rising.  Mark this new level.

6. The distance between your two marks indicates how close to the top of sump the theoretical maximum water level could be set when the system is running

7. In practice you need to allow a couple of extra inches:-  to allow for small changes in flow rates, and for the fact you don't want the water lapping at the sump's brim in the case of pump / power failure.