The running-in phase
In the running-in phase, numerous algae will fight for predominance in your aquarium, spreading abundantly. As a result, the aquarium will acquire a quite unsightly appearance during this period. This is a normal process and no cause for concern. Diatoms, which produce slimy brown coverings, generally become established particularly quickly. A brown covering to which tiny oxygen bubbles are attached appears over the bed and living rocks.
During this phase, the prevailing conditions are highly unfavourable for corals and other invertebrates. They would fail to acclimatise, and would actually perish for the most part. These algae need a great deal of silicic acid in order to grow, however. As soon as the supply of this substance is exhausted, they will diminish of their own accord. The macro-algae which you have added are of assistance here, competing with the undesired micro-algae. If the algae coverings become too extreme, they should be extracted with a thin hose during the weekly water change or removed by mechanical means.
The running-in phase sees a propagation of filtering bacteria which convert ammonium into nitrite and nitrite into nitrate. For a time, there is a risk that while the first step is completed the second step is still in progress. The water is then toxic for aquarium dwellers, because it contains too much nitrite. You can check the nitrite level quite simply, using a standard test solution. If you follow our recommendations for running in your Cube, experience shows that you will not encounter raised nitrite levels, however.
In the first few months there is always a danger of one or more undesired varieties of micro-algae spreading excessively.
Brown diatom coverings generally recede of their own accord after a short while, but other algae, such as red slimy algae or green thread algae, can be very persistent.
Do not overstock your aquarium
Avoid overfeeding, temporarily reduce amount of feed if appropriate
Replace part of the water (15 %) on a regular basis
Keep density in the normal range (1.022 – 1.024)
Extract micro-algae or remove by mechanical means