Can I divide this tank into different environments?

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One of our readers asks if they can split their tank into two environments - one side with smaller fish and the other for Reedfish or puffers...

Q) I am setting up a 360x60x60cm aquarium and I’d like some advice on what to fit it out with, please. The plan is for it to be well planted and have a modest amount (relative to its size, anyway) of small fish. What sort of filter would be best?

I wondered whether, given the large size, I could have a heavy flow in one area for the fish that like it, or maybe divide it into two so that I could keep the smaller fish at one end of the tank and maybe Reedfish or a puffer at the other — what do you think?

Finally, can I use builders’ sand, rather than aquarium sand, as a substrate?

VIKTOR WYND, VIA EMAIL

A) Neale says: There’s no single ideal filter for all situations. External canisters provide the most ‘bang for your buck’ but are fiddly to set up and will take up space under the tank. Internal canisters are much easier to use and maintain but, being more visible, they take away from the overall scenic effect of a planted tank. I’d be tempted to look at adding a sump (take a look at some of the off-the-shelf marine tanks with built-in sumps to give you an idea). These don’t just add extra water volume to the aquarium but also give you somewhere to install bags of biological media, and even the heater, meaning the display tank can be left uncluttered.

I’d tend to choose either fish for brisk water currents or fish from sluggish environments, rather than trying to mix them both. While a large tank could be designed to have patches of faster and slower water currents, what you’ll find is muck collects in the more sluggish areas, quickly becoming unsightly. If you want a big tank with small fish, moderate water flow is probably the ideal. Turbulent water currents aren’t compatible with many plants. Some love it, such as Vallisneria, but others, like Hygrophila and Cryptocoryne, aren’t so keen. So, pick the plants as carefully as you pick your fish.

Builders’ sand is a bit sharp to use with fish that like to burrow, and I’m not sure it is guaranteed to be lime-free. Luckily, pool filter sand and gardener’s silver sand are both smooth and lime-free, and both make inexpensive alternatives to aquarium sand. I’ve always used gardener’s silver sand for biotope tanks. As it ages the colour softens a bit, where I suppose algae and bacteria coat the grains, cutting down on its shininess.

Separating a tank into two compartments using plate glass or similar is not recommended. Supposedly — although I haven’t tried it out — it can cause unequal pressure to develop, that makes the tank more likely to leak or even crack. While egg crate can be used to separate male and female cichlids without such problems, in your tank it wouldn’t stop the small fish swimming through the egg crate into the carnivore’s half, so I can’t see that working too well. In any case, Reedfish are an absolute pain to maintain in an aquarium that isn’t sealed up as tight as a drum, being naturally amphibious animals that slither into wet grass during the night to hunt for prey.