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    Cycling New Rocks and Tanks

    Written by: tHEcONCH


    Cycling rock and tanks can be a bit of a mystery for beginners. Cycling and the 'Nitrogen Cycle' are pretty well covered by other sources, but the other stages that tanks and rock usually pass through at the same time aren't often mentioned and can cause a bit of anxiety to those starting out. 

    Many books and internet threads refer to using 'live rock'. Overseas you can buy 'live rock' which has all sorts of marine algae, bacteria, and little critters on it which greatly speeds up the process - here in New Zealand most of us have to make our own from dead coral rubble as we cycle up the tank. I have recently started a new tank and thought it might be useful for some of you to see pictures of the stages new rock and tanks usually go through so that you understand what is happening and don't panic too much. I will add to this as time passes and the rock matures into proper live rock with marine algae and random flora and fauna. 

    The rock in the picture was 'cooked' i.e. kept in an unlit tank of saltwater for a few weeks to kill off/remove as much of the (decomposing) organic matter as possible, then placed into a brand new tank with all the circulation pumps and lighting on. You can use uncooked / uncured rock (its cheaper and you can get underway immediately), but that will also increase the severity of each stage which will in turn greatly extend the time taken to progress through each stage (I'd tripple the indicative times I've given below)

    Stage One:

    The rock is still mostly bright white, devoid of pretty much anything living other than Diatoms which have begun to colonise on the parts of the rock exposed to light (they are photosynthetic organisms). The nitrogen cycle is just beginning. Correspondingly the water values for the tank read Ammonia 1ppm , Nitrite 0.2, and Nitrate 0. Expect this stage to be reached after about 3 days.


    Stage Two:

    The rock is now covered in a thick layer of Diatoms. Bubbles rise up from the rock as a by-product of photosynthesis. The water is rather hazy and the water values for the tank read Ammonia 0.1ppm , Nitrite 0.2, and Nitrate 1. Expect this stage to occur from 5 - 10 days, and to last upward of a further 2 - 10 days depending upon the quality of your equipment. 


    Stage Three:

    The Diatoms have begun to receed as they have exhausted the nutrients in the water. Tiny Copepods have been introduced to the tank through a small amount of 'live sand' and have begun to colonise the rock. The water values for the tank read Ammonia 0ppm , Nitrite 0, and Nitrate 1. The tank and rock are now 'cycled' and ready for livestock. The time taken to reach this stage will depend upon a number of factors, but most tanks will take about two weeks - others with less powerful skimmers, circulation and light may take closer to a month or even longer if uncooked / dirty rock was used. 

    The first water change should now be made - if you do one prior to this then your water parameter readings will be more favourable, but your population of beneficial bacteria will also be small, causing the process to restart (mini-cycle) once the first livestock is added.



    Stage 4:

    Corals have now been placed temporarily on the rock so that they can be observed and repositioned if they show signs of stress (from unsuitable light, flow, or other parameters). Mushrooms (Coralimorphs) and Zooanthids are a good choice at this stage as they are relatively hardy and can tolerate fluctuations in water quality. A few Diatoms remain, but simple forms of green algae are now appearing on the aquarium glass and filamentous green algae has begun to grow in some places on the rock. The green algae will remain from anywhere upward of a month, and in many cases never completely goes away. Although unsightly, having some green algae in your tank is not necessarily a bad thing as it provides shelter for small organisms and food for some sorts of fish. It will, however, complete with Coral for light and space and needs to be kept in check.


    Stage 5:

    Fish and more corals have now been introduced to the tank. All water values are still favourable, however the influx of nutrients in the form of fish food, fish poo, and slime form corals has resulted in Diatoms and reddish coloured Cyanobacteria reappearing on the rock, and a think layer of Diatoms have reappeared on the sand. Although your tank and rock is cycled it is important to keep testing for Ammonia and Nitrite as the sudden increase in the bio-load on the tank can cause spikes or a 'mini-cycle' as the growth of the bacterial colonies lags behind the increase in polutants. Be prepared to reduce feeding and make water changes if either are detected at more than a trace level. This stage will last anywhere between 3 - 5 weeks depending upon your equipment and the number of fish introduced, feeding etc. If you want to speed things up a little, syphon up the 'mats' of Diatoms and either discard, or wash in freshwater and return the sand to the tank.



    Stage 6:

    Coraline algae has begun to displace the diatoms, cyanobacteria, and green algae. The corals have also improved in colour, indicating that water and tank conditions have largely stabilised. Expect this stage to take upward of two months to be reached. Assuming regular partial water changes are made and water parameters are maintained at correct levels, the coraline algae will continue to grow and the rock generally 'clean up'.

    A footnote:

    Cycling means using new rock or dry rock basically the bacterial population has not established fully. The idea is that the cycle must complete ie the bacteria population must reach maximum stable levels. Cycling can occur in the dark or under light.

    Cooking (hate the term personally) consists of taking live rock out of an existing tank. ie it is still alive and placing in a dark container with good skimming and circulation. The idea is that nuisance algae will die off and the beneficial bacteria gets a chance to catch up and consume all the nutrients in the rock.

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