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Aquarium Fish FAQs

The Rock ‘N’ Critters team are among the UK’s leading marine aquarium experts – if you have any questions about your aquarium or the fish who inhabit it, we are the people to ask! We’ve answered some of our customers’ most common questions below; if you’d like to submit a question that isn’t answered on this page, please don’t hesitate to get in touch.
When can I add fish to my aquarium?
To protect your fish from ‘New Tank Syndrome’ – illness due to being placed in water that hasn’t yet had time to build up enough good bacteria – we and most other aquarium experts recommend a method called fishless cycling.

Before you add any fish to your tank, you will need to add bacteria in the form of filter maturation fluid. You will also need to add an ammonia source to feed the bacteria. Use a testing kit to test your water regularly, and don’t add any fish until there’s enough bacteria in the water to break down the ammonia you’re adding.
How often should I change my aquarium's water?
It depends on the size of your aquarium and what kind of fish you have – some fish are messier and need their water changed more often than others.

As a ballpark figure, we recommend a 25% water change every two weeks. Leaving the same water in the tank for too long will make your fish more vulnerable to disease.
What is the best lighting for a marine aquarium?
The best lighting for your aquarium depends on its inhabitants. What kind of fish do you have in your tank, and are there plants and corals keeping them company in there?

We offer a huge range of aquarium lighting products here at Rock ‘N’ Critters – if you’re not sure which is the best option for your aquarium, please feel free to contact us and we’ll be more than happy to help.

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