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.

Skimmers and Plankton

Despite my skimmer runnung 24/7 and producing very satisfying amounts of brown gunk it appears that plankton levels are unaffected. Common knowledge has it that skimmers remove plankton - it makes sense, it seems logical and therefore it must be true!

However, after reading a post in another blog where a temperate reefkeeper in Oregon, USA, employed a skimmer to remove plankton blooms from his tank with little or no success I began to wonder if plankton is somehow 'immune' from skimmer uptake. It may be worth examining skimmer gunk under a microscope to see if it contains live plankton. I have no doubt that soluble proteins are taken up by the skimmer, but if live plankton doesnt fall under that category, if plankton does not 'stick' to air bubbles and simply passes through the skimmer unharmed - this has major implications for all reefkeepers. It explains how coralline algal growth is able to colonise tropical systems despite heavy skimming, how squirts and those tiny little tubeworms are able to multiply and cover the backs of all those rocks and how undesirable algaes are able to spread.

If skimmers do not remove plankton then they have no apparent drawbacks whatsoever. At least in any system that requires plankton to feed filter feeders such as bivalve molluscs, non-photosynthetic corals and fan worms.

Perhaps native reef aquariums, benefitting from regular re-seeding of plankton from fresh seawater under optimum conditions may find that the keeping of soft corals, bivalve molluscs and other filter feeders may prove relatively easy. If native planktonic organisms are able to reproduce and thrive in our aquariums despite heavy skimming - as appears to be the case - it seems that it may well be worth considering using a plankton tow net and specifically looking to capture plankton to add to the aquarium in the hope that desirable plants and animals might therefore be propagated.

If plankton growth is a problem, green water etc, adding more filter feeders might prove the best way to control water clarity. A full - grown mussel filters 4 1/2 pints of water a day, adding a few dozen to a geen tank might prove far more effective than upgrading a skimmer.

Cycling?

Any experienced aquarist will be familiar with the need to cycle aquariums before adding any fish. The impatient novice has often learnt that its a costly and heartbreaking error to get overexcited and start adding large numbers of fish to a spanking new aquarium before bacteria levels have risen sufficiently to cope with the waste generated.

The vast number of aquariums in Great Britain are tropical, either fresh water or saltwater. We use synthetic seawater, buy inert coral sand and maybe a couple of cupfulls of same from an established aquarium, a few kilos of 'live' rock, maybe add a starter culture or, perhaps more commonly, a damsel fish ot two and monitor the Ammonia, Nitrite and Nitrate levels until more stock can be added.

If you plan to keep native marines under similar circumstances you will have to do the same. I have seen native marine aquariums with coral sand, rockery rocks and synthetic seawater. Apart from the fish and prawns nothing is wild. This set-up will take time to mature and will need cycling, a considerable amount of time, before its ready to receive more livestock and the unfortunate pioneering inhabitants may not survive the process.

However, if you collect fresh, wet sand, mud or gravel, to a depth of at least 2" for the bottom of the aquarium, use planted, fresh live rock and natural fresh seawater you can add livestock immediately. With sensible stocking levels and all the usual methods employed in maintaining good water quality it will be noted that Ammonia, Nitrite and Nitrate levels will be undetectable from Day 1.

I believe that its possible that waste products enter the food chain immediately, a vast number of organisms present in fresh seawater and sand/gravel take up uneaten food, waste and excreta etc. before it has a chance to mineralise to ammonia. What is left is easily dealt with by the more familiar bacteria and resulting nitrate is taken up by algal growth anyway. It may be that simply by access to fresh products we are able to introduce a far more diverse and dynamic microfauna to the aquarium allowing us to stock far more quickly than may be possible in tropical set ups.

If time, money, and space allowed I would like to try to gather some kind of firm scientific evidence for what is, at the moment only a theory. However, it is my experience that following the methods advocated in this blog its possible to stock sensibly as soon as the water has settled and never record any detectable nitrogenous compounds.

Seeding Tanks - Plankton

The new jetwashed Purbeck stone I added to the tank a couple of weeks ago has, in places, developed a nice growth of green algaes, grazing by snails keeps down hair algae and entero-type growth whilst some broader leaved sprouts have appeared as well as a few branching red algal growths. Its hoped that coralline algaes will eventually predominate.

To allow the maximum potential for new organisms to colonise the tank its necessary to carry out water changes, adding fresh seawater at fortnightly intervals increases the chance of catching planktonic spores and larvaes during their often brief time as plankton. Various animals and plants release spore and larvae at different times of the year.

Obviously using a plankton net with an aerated collection bucket allows far more plankton to be captured and introduced to the aquarium. A few problems have to be overcome to achieve this: open water is better, a boat is useful. A power supply to keep an air pump going - a car battery starter with a 3 pin socket outlet is enough to power a pump for 2 or 3 hours and if possible a cool box to transport the plankton on any car journey, die-off is rapid at elevated temperatures.

I keep an aerated bucket of phytoplankton to allow regular feeding of the mussels and cockles, although the aquarium has a healthy plankton population anyway, I am of the opinion that its a good idea to keep the aquarium seeded with new infusions.

The skimmer will remove a certain amount of plankton, this is inevitable and perhaps the only downside of skimming a natural aquarium. However, the benefits of skimming, in my opinion, far outweigh this drawback.

It is possible to entirely populate an aquarium using only seawater. Algaes and crutaceans, sponges and soft corals are propogated via planktonic cycles in their lives. Mussels in particular are early colonisers of new habitats, during WW2 dykes in Holland were damaged by Axis bombing flooding certain areas. When the dykes were repaired after the war and the land was pumped dry again mussels were found hanging from previously submerged tree branches and the eaves of houses! Under the right conditions this can be replicated in a captive enviroment. A refugium, with only a few rocks and some sand or gravel, will, over time develope a population of plants and animals entirely from the addition of fresh seawater. Its an interesting diversion and worthy of study as a seperate entity from the main display tank.

More pics

The new lights shortly after installation/

Spiny starfish

Montagues Blenny

The left hand side of the tank

The Goldsinny seen here looking out of one of its caves, the sharp teeth can be seen

New Pictures

The Goldsinny chabges colour rapidly, when excited for any reason it adopts the spotted colouration seen here. In this case a mussel has been opened and dropped into the tank. The smaller corkwing wrasse often shadows the larger wrasse whilst the mullet and 2 spot gobies hang around hoping for scraps.

Here the strawberry anemone can be seen next to a mussel bed with the corkwing wrasse

Beadlet anemone

Biological Balance

I'm not entirely sure that the title of this post is really right, but I'll plough on regardless and hope that all becomes clear. Those of us who have kept tropical marines will be familiar with the basic nuts and bolts of the Nitrogen Cycle and will be obviously tempted to assume that the same principles apply equally to native/temperate systems. However, it occurs to me that there may be some differences that might be worth exploring.

This is purely hypothesis, I would welcome discussion, either backing this up or refuting it. As such I may well ramble, I may be entirely wrong, but whatever the case I believe its worthy of discussion.

Firstly there are fundamental differences in the nutrient levels of tropical and temperate enviroments. Speaking extremely broadly it seems to be an established principle that tropical reefs are nutrient poor. I've never been entirely sure what this actually means! However, it also seems equally established that cold water ecosystems are nutrient rich. I understood this to mean that cold currents upwelling from the deep carried minerals and nutrients to the surface providing food for massive plankton growth which fuels some of the largest bioloads on the planet. Wherever these currents rise to the surface - the West Coast of South Africa, the East Coast of South America, the West Coast of North America vast numbers of fish, birds, whales etc benefit. I dont know what these nutrients are - organic or mineral? Whether the term 'nutrient' is accurate or not it is a term often heard on Nature Programmes on the television when describing the rich food chains of the places mentioned above.

Anyway - what does this have to do with native marine aquaria?

Tropical marine aquaria are geared towards nutrient export, to approach the conditions found on tropical reef crests it is obviously necessary to do so. As tropical aquaria in the UK and North America are almost certainly required to use synthetic seawater, inert coral sand and 'live' rock that has been cured (ie all dead and decaying organic matter removed) they start off with only the hardiest bacteria and microfauna to carry out the biological processes of nitrification and denitrification, phosphate reduction, detritus mineralisation and everything else. In many cases this seems to be adequate, successful tropical reefs are attainable and well documented. All seem to employ live rock and nutrient export.

Deep sand beds, filters, mineral additions, 'miracle mud', refugiums, skimming, water changes, water movement, detritus removal, careful husbandry and lighting in a myriad combinations and variations all play a part in successful tropical reefkeeping.

Temperate reefs do not have the benefit of live coral rock, many of the rocks found around our coast are impermeable, essentially inert with no buffering capability and provide no habitat for bacteria other than the surface. Likewise the sands and gravels found around our coast are often silica based, in a tropical aquarium such rock and sand would be deemed utterly useless as a substrate for carrying out the nitrogen cycle. Yet the mineralisation of organic waste still occurs effectively. It seems possible that other processes are at work here. This is where I get on to very shaky ground!

My tentative theory is that effective mineralisation is carried out in captive native systems by multi-celled organisms as well as bacterias. We dont have the vast surface areas utilised in tropical aquaria using coral sands and rocks. Whilst Nirobacter and Nitrosomas bacterias are undoubtably present in significant amounts there is simply not the same surface area for them to colonise. I notice that the sand bed of my tank, collected at low water and transported directly to the aquarium was dark just an inch or so under the surface. As it has settled and matured there are myriads of tiny tunnels throughout. Vast numbers of worms, too small to be visible to the naked eye are present. What other creatures also live in this sand? What do they eat? What processes are being carried out? Are similar organisms present in tropical aquaria? I believe that these organisms may not survive prolonged exposure to travel and collection trauma. In a native reef we are fortunate to be able to transport them alive and well by rapid transit. I believe that the presence of microfauna of many different species in a native captive reef are in some way facilitating all the biological processes necessary to effect mineralisation of organic waste to end products suitable for plant take-up.

Therefore, it seems that a fundamental difference in 'nutrient' utilisation is apparent between tropical and temperate systems. Temperate systems may well need nutrient retention within the food chain. Tropical systems are geared towards nutrient removal from the system.

Thats probably enough to be thinking about for now. I'll have more to say on such fascinating topics as detritus later.

Its low tide at Osmington Mills in 90 minutes and the family are ready to go rockpooling. More topshells are needed!