Native marine aquaria are pretty scarce. Little information exists on how to be successful in maintaining healthy coldwater marine systems in domestic aquaria.

Hopefully this record of my failures, triumphs and ideas will assist others interested in keeping some of our fascinating, beautiful and often little known sea denizens in aquariums.

Monday, 5 September 2011

Detritus and Design

If you keep a planted aquarium you will generate detritus in the form of decaying plant matter. Native algaes have cycles of growth and subsequent die-off, almost as land born deciduous plants flourish and then retreat according to seasonal cycles.
This presents significant challenges to the temperate reefkeeper. Pump intakes in particular will be prone to clogging seriously impacting on the efficiency of such items as skimmers, powerheads, circulators and especially canister filters. To a certain extent we can design the system to avoid this clogging or alternatively to facilitate the effective removal of detritus. On my 1st native marine system I built a 3 stage sump specifically to allow removal of detritus. The 1st chamber held the skimmer intake, the 2nd chamber was a lit section with a plenum and 4" of live mud to effect nitrate reduction and the 3rd contained filter pads through which return water drained before being pumped back to the system. It was rather flawed, looked OK on paper, but in practice the high flow (2 x 6400 lph Ocean Runners) blasted the mud away instantly leaving only gravel, the filter pads were continually becoming clogged causing the pumps below to be starved of water and fish were often found flapping on the filter pads having been washed through the system.
I learnt a number of lessons by the failure of this design:
  1. Weirs need to have slots cut into them to strain out fish and larger items of detritus
  2. Keep the circulation to the display tank, its generally not necessary to have 13000 litres per hour running through the sump!
  3. Use power heads or circulators to move water in the display tank instead of relying on massive return flow.
  4. Use the 1st chamber of the sump to catch detritus and move the skimmer to the middle or end chamber, there will be far less risk of the intake becoming clogged.
  5. Use natural methods of detritus utilisation rather than employing mechanical methods that will require endless maintenance.

My current system employs a slotted weir, it has proved effective at keeping even the smallest fish in the display thank whilst allowing fine vegetable matter through. Larger algal break -offs are easily removed by hand when convenient.

I use a 10 gallon settlement tank as the 1st chamber with an 1 1/2" overflow to the main sump. A layer of sintered glass filter medium on the base of the settlement tank catches and holds fine detritus where colonisation of detritivores and bacteria is encouraged. It requires no maintenance for many months at a time - if ever.

The main sump, a 3' x 2' x 2' glass aquarium contains the chiller pump and return, the skimmer and the main circulating pump. The base of the sump has a 2" layer of shells collected from the beach. This traps any remaining sediment. I keep 6 oysters in the sump to filter the water further and additionally about 30 tiny prawns have found their way here and catch any food particles that end up here. I have no problems with any of the pumps clogging and the slower flow rate of 1300 lph allows even the finest sediment to settle. A population of amphipods and copepods has colonised the sump and is presumably feeding upon the sediment. Apart from adjusting the chiller temperature and emtying the skimmer no maintenance is required for many months at a time - if ever.

Therefore, rather than engaging in detritus removal I have concentrated on utilisation. Whilst larger items are removed from the weir once a week or so, all fine particles are encouraged to settle in the 2 parts of the sump assembly. Colonies of detritivores will undergo some recirculation back to the display tank and provide food for the inhabitants but generally the low flow rate allows a stable oxygen rich enviroment for copepods and amphipods to thrive. This is as close to nature as I am able to get. In the Ocean as plankton dies and sinks to the bottom vast numbers of microfauna exist to feed upon this 'marine snow', seeded by the live sand in the display tank a similar habitat in the sump should, in theory, develope and feed upon the detritus. Soluble protein waste generated by this process can be removed by the skimmer or undergo mineralisation on the surface area supplied by the sintered glass in chamber 1 or the shells in the main sump.

I could place a few inches of live sand in the sump as well, but the sand in the main tank is probably the main filter of waste in the system. I am interested in seeing what the colonisation of the sump consists of and have elected not to introduce microfauna deliberately. As mentioned previously I hope that sponges and squirts colonise the sump, lit only by a small blue LED no photosynthesis occurs in the sump and algae cannot grow there. It is hoped that the sump will mimic a deepwater enviroment and perhaps in time will prove every bit as interesting and colourful as the main tank.

So, the design of this, my 3rd native system, has been optmised to require very little maintenance indeed whilst providing habitats for a range of organisms from brightly lit rockpools and shallow shores and also a similar sort of habitat to that found below piers and jetties. I cannot mimic the great pressures found at depth, but am unlikely to ever find deepwater specimens anyway.

I have tried out other forms of detrituis removal. My 2nd system, featured in the 1st year or so of this blog had no sump and intakes for the skimmer and chiller were in the display tank. I had endless work in keeping the intakes free of vegetable matter, the chiller and skimmer frequently became so clogged they ceased to function and the use of flourescent lighting ensured that the keeping of plants was always a battle unless I kept a strict regime of expensive bulb changing. I tried using canister filters to remove waste but once again the intakes were frequently blocked. Without constant maintenance, uncoupling the filter and washing it out, going through the immensely frustrating cycle of trying to prime it again and make it work - only to have to clean it out again a few days later, the filter simply didnt work. I spent a huge amount of time and money trying to utilise canister filters and whilst they are probably great in unplanted fish only systems I feel that they are largely a cumbersome hassle in any kind of planted native reef. However, filled with activated carbon or Rowophos they do have a place in clearing water or removing specific pollutants on a short term basis. As a long term solution to water quality they have significant shortcomings however.

The amount of detritus generated can be minimised by good quality lighting allowing algal growth to be sustained. Little is known about the life cycles of many macroalgaes and many will undoubtably die off and regrow according to the seasons even under constant lighting and temperature. It is probably unavoidable that these cycles will occur no matter what, but good lighting and flow will almost certainly keep die-off to natural cycles rather than death by unsuitable habitat.

Whatever system a native reefkeeper employs it makes for a far more enjoyable hobby if the system design allows for minimum maintenance whilst allowing the maximum number of organisms to be kept in optimum conditions with the least chance of system failure due to mechanical problems. Dealing with detritus waste is critical to system health and your own enjoyment of your aquarium. Keeping it as natural and simple as possible will go a long way to keeping native reefs a pleasure, not an irksome chore.

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