Running-in or initial phase

Here’s how to ensure your aquarium has the right start – the important running-in phase

Once your aquarium is set up, water has been poured in and the technical equipment is running; then only the microflora for it to work biologically is missing.

Sometimes it is recommended to wait just a few weeks, before adding fish and invertebrates. But this approach bears the following risk: If running in the aquarium WITHOUT fish and invertebrates, beneficial bacteria hardly develop and reproduce in the aquarium because without fish and invertebrates there is simply no water pollution. But if you add them from the beginning the reproduction of bacteria lags behind and the water parameters can become critical, even leading to deaths (ammonia and nitrite; for more details, see Water values ).

We therefore recommend the following procedure, which we guarantee to work:

At least 15 minutes after adding the water conditioner JBL Biotopol please add JBL Denitrol (shake well before using). After a few hours the containing bacteria will have become active and start to break down pollutants and to reproduce. Now you can (and should) start adding the fish stock the next day and increasing numbers during the following days. As a consequence the bacteria are confronted with increasing water pollution and react by reproducing. At the same time the bacteria you have added prevent problematic water values (ammonia and nitrite values).

Please feed sparingly during the running-in phase, which normally lasts about one month, and carry out a weekly partial water change of about a third of the water content. Ideally carry out the water change with the help of a gravel cleaner ( JBL AquaEX Set 20-45 or JBL Aqua In Out complete set ).

Note: The use of antibacterial medicines will also kill the beneficial bacteria present in your aquarium. You will therefore need to reinoculate your aquarium with bacteria after the treatment, as you do for an initial setup.

What happens if you start your aquarium without a bacteria starter?

You will get some beneficial bacteria into your aquarium even without a good bacteria starter like JBL Denitrol . They get into your aquarium water with the plants, the decoration and even from the air. However, as your aquarium is freshly set up, the bacteria will come into a home with an empty fridge - they lack food! If you then wait two weeks, most of the bacteria will have starved to death, because no one is filling the fridge or no dirt is getting into the aquarium, which the bacteria live on. Only very few bacteria can survive without this food (the water load from fish and food). If you then test the water (NH4 and NO2) two weeks on, you will (still) not find any water pollution. Where should it come from? Then you put in a batch of fish and your few bacteria are completely overwhelmed. And sex with bacteria is complicated: they need a certain start-up phase (we know this from other creatures too...) and only then are there new bacteria. And it is precisely this start-up phase that leads to a problem: While the fish are polluting the water with their excretions as soon as they are introduced, and this water pollution is detectable using an ammonium and nitrate test, the bacteria are still in their cuddling phase, which microbiologists call the lag phase. In the worst case, the nitrite value rises above 0.4 mg/l, a dangerous to lethal level for fish. It is only a few days later that the bacteria have started to multiply and the amount of bacteria has adapted to the food supply. But by then it is already too late for the fish! It’s much better, therefore, to start with a good bacterial starter (Y JBL Denitrol ) right from the beginning and then gradually to stock the aquarium with animals. This is guaranteed to work without problems!

Bacteria starter for aquariums - waste of money or absolutely vital? Why activated carbon?

All you need to know about aquarium bacteria starters: Should you wait 2 weeks after setting up the aquarium or just use bacteria starter? What happens if you just wait and don't use a bacterial starter? What are the causes when problems occur? We explain how to successfully start an aquarium biologically.

A word about cookies before we continue

The JBL Homepage also uses several types of cookies to provide you with full functionality and many services: We require technical and functional cookies to ensure that everything works when you visit this website. We also use cookies for marketing purposes. This ensures that we recognise you when you visit our extensive site again, that we can measure the success of our campaigns and that the personalisation cookies allow us to address you individually and directly, adapted to your needs - even outside our website. You can determine at any time - even at a later date - which cookies you allow and which you do not allow (more on this under "Change settings").

The JBL website uses several types of cookies to provide you with full functionality and many services: Technical and functional cookies are absolutely necessary so that everything works when you visit this website. In addition, we use cookies for marketing purposes. You can determine at any time - even at a later date - which cookies you allow and which you do not (more on this under "Change settings").

Our data protection declaration tells you how we process personal data and what purposes we use the data processing for. tells you how we process personal data and what purposes we use the data processing for. Please confirm the use of all cookies by clicking "Accept" - and you're on your way.

Are you over 16 years old? Then confirm the use of all cookies with "Noticed" and you are ready to go.

Choose your cookie settings

Technical and functional cookies, so that everything works when you visit our website.
Marketing cookies, so that we recognize you on our pages and can measure the success of our campaigns.