On filling an aquarium / Or preparing one – part 2

Usually, when setting up an aquarium (especially for fussy fish like discus), one starts planning a month or so in advance. That leaves plenty of time to fill it up, and let the pump, the filter and the water get used to each other. There’s enough time for the chemicals in the tap water to lose their strength (please don’t ask me how – I have no idea), enough time for the right sort of bacteria to settle in, enough time for a mini eco-system to evolve – or at least for the water to get a green tinge!

We didn’t have that much time.

Instead, we hung the new filter into the old aquarium for a couple of days.

Usually, in an established anquarium, one changes about a quarter of the the water every 2 weeks (minimum). Ish. The water is syphoned out and replaced with fresh (tap) water. Officially the water you put in should have the same temperature as the water you take out but ours seem to like it a little bit colder – they swim in and out of the ‘jet’ like anything!

While we were setting up the new aquarium, we changed the water approximately every 3 days. We didn’t take nearly a third though, more like a sixth. We syphoned the water into the new aquarium instead of into the garden. The old aquarium was topped up and the process was repeated a few days later.

Once the new aquarium was about 3/4 full, we took the new filter out of the old aquarium and gave it a new home in the new aquarium.

We added the air-stones*, some wood for hiding behind, and a good handful of water plants and waited for the last water change.

Once the aquarium was full, and had been run though the filter for another couple of days, we were finally ready to transfer the fish.


Fish aren’t really good for the impatient. Unless they’re learning to be patient…


Even our accelerated set up took a couple of weeks. It was ok, but only just. If you have time for it, I would always recommend letting it settle down a bit more before adding the first fish. I think having ‘ready made’ aquarium water (from the old aquarium) is awesome, as long as you fish are healthy and happy. If they’re ill, and you buy new fish, I think I would rather wait longer and keep the aquariums separate.


Any advice welcome 🙂


*air is pumped through a porous stone ao that bubbles come out, circulating and oxygenating the water.

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