What's the best way to swap over tanks?


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A PFK reader is worried about transferring her stock to a new tank. Neale Monks is on hand to help.

Q. My tank has started leaking and cannot be fixed, so a new 54 l/12 gal. tank is arriving soon. I’m now panicking, as I’ve never changed tanks before.

I was planning a river/stream set-up, with bigger pebbles at one end, before being mixed with gravel and finishing with sand at the opposite end, with branches hanging from the glass into the water.

Can I do this using ordinary twigs and pebbles from the garden, and, if so, how would I clean them before use?

I want some natural looking sand too, but I’m worried about how to clean it first.

How do I introduce the fish to a tank with new filter media to avoid new tank syndrome?

I know it’s best to use the old tank water, but do I put the fish in the tank with the new filter and old water — or would the new filter still struggle to cope?

Hannah, email

A. It’s best not to use wood from the garden. Sprays, such as insecticides, soak into wood and that can be very dangerous to fish.

Fresh wood also rots quickly, developing fungal patches and bacterial slimes.

So, even if you get wood from somewhere sprays aren’t used, such as a forest, then you’d still have rotting wood. Stick with cured wood sold for aquaria.

If on a particularly tight budget, try untreated bamboo from a garden centre. You can silicone this onto glass or slate to prevent it floating and then bury the glass or slate under the substrate.

Have some of the bamboo going straight up and other bits more diagonal, yet all with their tips above the waterline. In this way you can create a really authentic swamp or riverbank effect that works great for all sorts of community fish.

Vallisneria, incidentally, looks great alongside bamboo because both have a long, tall shape.

Don’t use garden pebbles as many won’t be lime-free. They’ll mess with water chemistry, and seams can leach metals like copper that are lethal to fish and shrimps.

Buy 'pond-safe' pebbles from a garden centre and a 25 kg bag at my local shop costs around a fiver.

Garden centre smooth silica sand — sometimes sold as silver or pool filter sand — must be cleaned thoroughly before use. Rinse, rinse and rinse again! Even then, you’ll likely find the aquarium very murky after adding the sand. Simply do more water changes and rinse out the aquarium filter as often as needed.

If you have a mature filter, you may be able to simply remove the biological media and stuff it into the new filter. If you can half-fill a new filter with mature filter media, it’s basically cycled and good to go!

Failing that, connect both filters to the tank and have them running together for four to six weeks. But you may need to turn the flow rate down if the fish are buffeted by the current. After that time you can disconnect the old filter, knowing that this will have given time for the filter bacteria to colonise the media in the new filter.

Water itself only carries a few filter bacteria, so moving old water into the new tank won’t be enough to cycle the new filter. However, half-filling the new tank with old water will minimise any problems with pH or hardness variation, so is worth doing on that score.

Neale Monks

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