How do I prepare my tank for an extended holiday?

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Short holidays, of a week or two, are easily dealt with — provided the tank is well maintained and the fish in good health beforehand, they should survive without feeding just fine.

Q) I’ll be abroad for a five-week holiday in a couple of months’ time. My tank is 120x60x60cm with an external heater/ filter. It’s a heavily planted community set-up with CO2 injection. I normally do a 25% water change each week. It contains a mixture of fecund Platies and Bristlenose Catfish, plus Cardinal, Glowlight and January Tetra, Boesemani Rainbowfish and Corydoras. I can feed most of the fish via an automatic feeder and I might be able to get someone to occasionally feed the plecs with tablets and cucumber. I can also get some fertiliser into the tank while I’m away, using a Dennerle Dosator.

My main concern will be the filter and the absence of water changes and how I can prevent the water becoming toxic.  I was thinking of doing a 50% water change and a clean of all the filters just before I left. Should I also reduce the number of fish in the tank, maybe by giving them to my local aquatic shop, to reduce the demands on the filter?

PHILIP BURKE, VIA EMAIL

A) NEALE ADVISES: Short holidays, of a week or two, are easily dealt with — provided the tank is well maintained and the fish in good health beforehand, they should survive without feeding just fine. But anything longer than that can cause problems. It does depend a bit on the species, some predatory fish being adapted to going without meals for long periods, while algae-eating species may find enough to graze on if the tank lights are set to go on and off automatically.

With a mixed species community set-up, however, some sort of feeding will be needed. Automatic feeders can work well, but the problem is that humidity so close to the tank may cause the flake to lose its nutritional value over that period of time. Having someone trustworthy to feed the fish once or twice a week is better. If they’re experienced fishkeepers, this is an easy option, but if not, you could decant daily portions of food into airtight containers (the sort used for pills are ideal) and hide all the rest of the food away, to reduce the risk of overfeeding.

Assuming that the tank is sparingly fed — and I would recommend 2-3 day gaps between visits from the fish-sitter — healthy plant growth should keep the nitrate levels low. While this might sound like lean pickings to us, tropical fish are adapted to times of the year when food is scarce, and this won’t cause any problems at all. Some will eat algae, and I dare say a few platy fry

will be eaten as well. But otherwise, they’ll be fine. I’d clean the filters several days before you leave, just in case there’s a problem. You’ll feel less worried if you’ve seen the tank running normally for a day or two after you’ve carried out the maintenance, and you can feel safe in the knowledge that things such as the external filters are connected properly without any leaks.

Some aquarium shops will look after pet fish during holidays, but the flip side to this is exposure to parasites and other infections. Most aquarium shops are hooked up to shared filter systems, and while some include things like ozone and UV sterilisers to minimise the transfer of pathogens between new livestock and those already in the tank, this isn’t always the case. There’s also the stress that results from moving fish. Territorial species will be upset by being turfed out their homes and forced to establish new territories in new tanks, while schooling species cooped up in a smaller tank compared with their home aquarium won’t be happy either. So, while I can see the value of ‘holidaying’ your fish at a trusted retailer in some situations, for example where delicate or difficult to feed species are concerned, it’s not my favourite solution to this problem.

Basically, if the tank is well run and the fish well fed, a few weeks on limited rations via a trusted fish-sitter is probably the best way forwards. The risk of starvation is minimal, and provided the filter is maintained beforehand, and the food put into the tank tightly rationed, the risk of dangerous high nitrate levels accumulating is very low. I might be tempted to switch off carbon dioxide fertilisation if I thought there was a risk of pH instability without daily checks, but you’ll know the tolerances of your automatic dosing system better than me. Switching the thing off won’t harm your plants across a few weeks, even if it isn’t ideal, and likewise, going without mineral fertilisers for a couple of months isn’t the end of the world for them either.