What’s safe to spray around my tank?

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Are there any fly sprays or insect killers that can be safely used around an aquarium? A reader asks...

Q) Are there any fly sprays, insect killers or air fresheners that can be used safely anywhere near an aquarium? I know someone with an itchy trigger finger!

DAVID JENKINSON, VIA EMAIL

A) Neale replies: So far as fly sprays go, unfortunately, no. The ingredients used in most of them, typically things like prallethrin, permethrin, and eucalyptus oil, are all toxic to fish. How quickly they’d kill your fish is open to debate. A bigger tank will dilute the insecticides more effectively, but on the other hand, any fish that breathes air, such as Corydoras or gouramis, will be exposed to much higher concentrations, and therefore more likely to be harmed. So, it’s very difficult to say for sure whether a quick blast of bug spray will wipe out your community in one fell swoop. But on balance, the risk is there, and it’s not worth taking.

Air fresheners are a bit of a mixed bag. It’s very hard to be sure without knowing what sort you’re talking about and how often you plan on using it. The slowly evaporating block-types probably don’t do much harm, though I’d avoid putting one right next to the tank and would not use them at all if I was keeping sensitive air-breathing fish, such as Betta species. But aerosols are riskier, and while the odd squirt probably doesn’t do much harm, it’s hard to know for sure without studying the formula of the aerosol in question. In my salad days, I’ve been known to burn the odd joss stick in my college dorm alongside my fish tank, and it didn’t seem to do any harm. But I’d be a bit more careful nowadays, especially with sensitive fish, and particularly those that gulp air periodically.

On balance, it comes down to confirming with the manufacturer that their product is safe to use around fish. Unless said manufacturer can confirm that is the case, it’s best to err on the side of caution.