Refugia
Introduction
The basic idea behind a refugium is to provide a refuge or breeding area for animals which could not survive in the main tank, or are food for the main tanks inhabitants. Refugia may also be used as filters by adding Plants and substrate of differing methods. I will elaborate on most of these methods below.
Refugia come in many forms:
1) Plant scrubbers
2) Mud filters
3) animal refugia
Algal Turf Scrubbers
In Algal Turf Scrubbers, filimentous turf algae is used to bind harmful compounds from the aquarium water into biomass which you then harvest and remove from the scrubber, on a regular basis. Some of those compounds removed are, heavy metals, SiO2, NH3 and NO3; although the algae has to convert NO3 back into ammonia to use it as food. For a more detailed description of what algae will utilize, read Dynamic Aquaria by Dr. Walter Adey and Dana Riddle.
Algae also will release almost anything it removed from the water, back into the water, if you let it die and do not remove it from the scrubber, or feed it to a fish-- as the fish will, of course, excrete the waste back into the tank, as well as absorb the toxins/compounds bound in the algae which can damage its viscera. Algae will not however, remove DOC's very well, infact it will produce them, as the water is yellow in algae scrubber only systems. Algae also release algal spores which can attack corals and grow in undesirable places, these two problems can, however be prevented by the use of a protein skimmer as it will remove both algal spores and DOCs.
Some have said that if water conditions are correct for algae growth in the scrubber, they are correct for its growth in the tank and will grow there. That is not true if you use this method correctly, which is to make conditions for the algae in the scrubber better than those in the tank, and so the algae will grow in the scrubber, and, if the scrubber is sized correctly, the algae will grow so profusely in the scrubber, that all/most of the nutrients can be bound in biomass as fast as they are being produced and so none will be left for any algae in the tank. To do this, use a large scrubber, with a surface area close to that of the inside of the display tank. Yes, this is QUITE large, but to get this to work, it must be of that relative size and rather shallow as well.
The surface area can be increased by:
1) Eggcrate and screening
2) acrylic plates set on a 45* or so angle
3) acrylic rods
Current/flow rates
You need good flow in Algal turf scrubbers, 250-300 GPH for every 6" deep square foot of scrubber area. This will provide sufficient contact time between the water and algae for adequate removal of harmful elements.
The scrubber should be shallow because you need a fair amount of current and light penetration to allow for thick and healthy algae growth, and you must get the nutrients to all of the algae as well for this to work as efficiently as it could.
The current is produced by either;
1) a dump bucket; which is not very practical as it can stop moving and overflow, and also it splashes and makes a lot of noise
2) a siphon surger; this has no moving parts to overflow, and will not overflow if constructed correctly,but as a result of continuous starting and breaking of a siphon, it is rather loud. For a diagram, see the end of this document
3) plates positioned in the way of the water flow so as to produce numerous eddie currents
4) Powerheads in the scrubber
ATS styles
There are many ways to skin this cat, here are some of them:
1) Dump bucket turf scrubber
2) Flow scrubber
3) Full algal refugium
4) Channel MMS
5) Macro algae scrubber
Dump bucket turf scrubber
The water level in the dump bucket turf scrubbers should be about 1-3" when the bucket is dumping.( see fig. 1) The scrubber in fig. 1 uses a HID bulb to provide light. Notice the surger device empties onto a slanted screen and therefore has different water depths and different current strengths in different locations to allow a more varied array of algae growth. This scrubber is mainly intended for filimentous algae and not macro algas such as Caleurpa.This style is very efficient, as water surges over the algae, the algae absorbs nutrients, then it is exposed to CO2 which supercharges the algae's ability to remove things as it metabolizes the wastes faster. This could be compared to the efficiency of a trickle filter Vs. a UGF.
Flow scrubber
In a flow scrubber water constantly flows over plates covered with algae, so the water is in constant contact with the algae. Since it is exposed to less CO2 than the Dump scrubber, it is less efficient. You could easily remedy this by connecting its intake to a Carlson surge device, since this design has more surface area than the dump scrubber, it would be more efficient. However, this is not its typical application. The water level is 3-7" for flow style scrubbers( see fig. 2) In the flow scrubber below, figure #2, the flourecent bulb provides light for the algae that grows on the slanted plates. You can use any kind of plant lighting on scrubbers, not just flourecent tubes.
Full algal refugia
In this type of scrubber, both macro and micro algas grow. This will not filter very well due to the fact it has poor surface area, it is better at growing shrimps or algae for food. One advantage to this design is, you can put mud in the bottom and plant the caleurpa in it, and possibly Mangrove trees. The water depth is 7+ inches deep for full algal refugia(see fig. 3), as it is usually a tank.
Channel ATS
Not shown as the design has been copyrighted by little ol' me. This is similar to the Channel MMS in the Mangrove/Mud scrubber section. (which I have had a copyright on for about half a year now.) This can be hooked up to a surger and it will be probably the most efficient Algal scrubber.
Lighting
You must use lighting that is predominately in the red, yellow, orange, green, and not the blue spectrum. Most algae prefer this spectrum depending on what depth it comes from, the closer to the surface the algae is, the more red, yellow and orange light it will need, conversely, the deeper it is from, the more blue it will like.And if you utilize a reverse lighting cycle, meaning when the tanks lights are off, and the scrubbers lights are on, the photosynthesis of the algae will use the CO2 respired by the algae in the tank and from the zooxanthelle in the corals, and will, therefore counteract low night time/morning PH (Sprung/Delbeek, The reef Aquarium vol.1). I feel that a 24/7 photoperiod is better as then the algae will never stop growing and absorbing nutrients.
The best lights for this purpose are either HID sodium lamps and mercury vapor or other halogen lights. The brighter the better, but not enough to heat the water to a significant degree or prevent algae growth. You may also use either incandescent or flourecent Plant bulbs.
Macro Algae scrubber
This is very simple. See algae scrubbers section. All of those designs, except for the surging ones, can be applied to this method. Most of the time, this is not used as a filter, it is just used to breed Tang or etc.. fish food. For a filter it will work ok. It operates on much the same principals as the ATS. Most of us use refugia with macro in it, and so we have a Macro scrubber built in.
Mangrove/Mud scrubbers
In this type of refugium, there is a 1-2"+ layer of mud in which Red or White mangroves are planted and water is moved through the refugium at a few hundred gallons per hour. Macro algas can also be in the filter as well. The mangroves will absorb nutrients and grow larger, and must be pruned on a regular basis. Some people report that their skimmers stop working after a period of time due to the mangrove trees removing most skimmable compounds. Some people do not have this happen, this would appear to be the case with larger skimmers, like the ETS and HSA. As time passes, the mangroves will remove wastes faster and faster until there is very little left.
The Mud is a very important part of the method, as it is very biodiverse. The Mud houses many types of bacteria, flora and fauna. It performs Nitrification and denitrification, as well as providing the trees with more nutrients and holding them up as well.
From my own experience, and from some very complete data I have recently seen, mangroves appear to be a significant factor in water quality when implemented properly, as they remove NO3, PO4 3-, SiO2, NH3/4, NO2 and raise the DO and lower the BOD.
Lighting
You can use anything from incandescent Plant bulbs, Flourecent Plant bulbs, to even HID bulbs, like High Pressure Sodium units. As with the ATS system, you would want to use a bulb with a predominately yellow, red, orange and green spectrum to facilitate growth. You may even use Natural sunlight if you have access to it. The Mangroves should be exposed to light at least 12 hours per day. You can use a 24/7 photoperiod as well, as it will be more efficient that way,since the mangroves are constantly absorbing nutrients. You should turn the lights off for 12 hours every few days to let the mangroves rest, or they, IME, will become unhealthy.
Current/flow rates
You should supply mangroves with about 2 to 4 times your main tanks volume in flow per hour to allow them to draw the necessary nutrients from the water, the flow rate depends on how many mangroves you use.. This is assuming you have the proper amount of mangroves, which is 1 to 2 per ten gallons(PTG). This equals about 20GPH per tree. This measurement I have found to be optimal at waste removal, but you could increase it if you wanted. If you use more than 1 tree PTG , you must speed up the flow, as there will be less nutrients to go around between the trees.
MMS refugium styles
I firmly believe that the mangroves should be separated from the main refugium, as then they will have optimal flow, substrate and lighting. Below are some basic types of MMS.
There are a few styles of MMS:
1) Simple MMS
2) Mixed MMS
3) Channel MMS
Simple MMS
The most simple MMS is a tank with mud on the bottom,(figure 4) as seen below. Basically the water goes in through the pipe at the bottom so the waste hits the roots first, then travels upward where it escapes. The large diameter input pipe is cut off about 5-6" above the mud so the substrate is not disturbed. The mangroves will be submerged for a while, but once they start growing, this will not be. It is best to use older mangroves with this style of refugium, as the wee trees do not like to have their leaves submerged. The roots are usually buried as well.
Mixed MMS
The next type of MMS refugium is a bit more complex, as it involves more than just mangroves and mud. This type of MMS includes Macro algas and possibly Live Rock, and is similar to what GARF is using ,seen below in figure 5. This refugium is more complete and performs 4+ types of Biological filtration, Nitrification(Live rock and Mud), denitrification (Live rock, possibly mud), Algal filtration (macro algas), and Mangrove filtration--in one unit, thus making it more complete than a simple Mangrove/Mud only filter.
Channel MMS
In this filter,(figure 6), there are a lot of channels for mangroves and Macro algae to grow in, there is also optional live rock here.In other words, this can be a Simple Channel MMS, or a Mixed Channel MMS As water flows through these channels it passes through successive meshes of roots where nutrients are absorbed with great efficiency because the water must pass through each set of roots and cannot bypass any tree.This is probably one of the most efficient units, but largest and most difficult construct. If you do not make it rather large, the roots will have no room to expand, this is, I feel, the only downfall of this design.
Animal refugia
An animal refugium is meant to breed animals for fish or coral food. These are just ordinary refugia. They may contain sponges, shrimps, worms, fish, nudibranchs, starfish, cucumbers or almost anything else you want to grow. This style of refugium can be used to grow copepods and other food creatures to allow them to float back to the display tank to be eaten by fish or corals etc..
Current/flow/size
It is good to have a refugium that is about 1/2 to 1/3 of your main tanks volume, which you flow between one and two times the main tanks volume through. In the light one you should have a few powerheads for circulation. In the dark one, you should keep a slightly slower flow due to the fragility of the animals there.
Lighting
You should use lighting that is appropriate for the animals you are trying to keep. For most of us, NO or VHO flourecents are fine.
Styles of animal refugia
Unlike with the other refugia that are used as filters, these do not need any fancy channels, or dump buckets or mud, these should be just like any other tank.
There are two main styles of animal refugia:
1) Light
2) Dark
Light refugia
In a lit refugium, you will have Live Sand, Live Rock, and possibly a plenum. You will find worms, corals, shrimps, fish, cucumbers, stars and almost any other kind of life. Below(figure 7) is a lighted refugium.
Dark Refugium
Below, figure 8, is a dark refugium with 3.5" Bio Barrels. Yes, it is a bio media. It is very large and has very low surface area. it is used for sponges and tube worms to grow on, among other things. You will find shrimps,crabs, copepods, isopods, nudibranchs and other things.This rather peculiar unlit animal refugia type would be used to grow Carnation corals, light avoiding sponges, Sun polyps and other interesting and typically not seen creatures that usually are missed and on the bottom of the live rocks. I have, however, found this type of refugia to be the most interesting given the atypical nature of its inhabitants.
This ends the article for a while, more soon.
Ian McDonald
Modified Carlson Surge device
The below surge device is adapted from the Carlson Surge devices'(Delbeek/Sprung, The reef aquarium, vol. 1) basic design, but I have expanded on it with my own modifications as well. The water enters through the tube on the right which has a 1/4" hole drilled in it to prevent back siphoning. There is a small tube in the upper left hand corner, that is the overflow tube, in case the main tube is blocked this tube will not let the water go any higher than it is and will empty into the same area as the main tube, to prevent overflows.In the lower left you see the main siphon tube, this is where the water leaves the surger. The water rises to the main tubes highest point and spills out of the tube into wherever you intend.
