TROPICAL
How should I dispose of old or expired aquarium chemicals such as test kits, medications and conditioners?
RUFUS THOMPSON-COX
NEALE REPLIES: This is a really good question, but as far as I know, there isn’t a consistent best practice to this one. As with human medicines being returned to the pharmacy where you got them, any unused or expired fish medicines you’d obtained from a vet could be returned to them, as they’ll take steps to ensure the medication is properly disposed of safely. But over-the-counter fish medicines are not handled in the same way.
Now, one reason for that is that the medicines we get without prescriptions are generally very low on the toxicity scale. Or rather, they’re the sorts of chemicals that oxidise or otherwise break down very quickly, unlike some of the persistent pharmaceutical drugs that are known to cause problems in rivers and lakes.
Another factor is that the medicines we use are often relatively simple compounds that, if you keep them in the dark and in a tightly closed bottle, will be useable for years and years. Most of the old school fish medications based around organic dyes are going to fall into this category, and for a long time were sold without ‘use by’ dates of any kind. They might become a bit lumpy as some of the chemicals settle out, but a good shake or stir until everything dissolves again should fix that.
Finally, some of the chemicals we use are generally regarded as having such low toxicity that by the time they’re diluted in the sewerage system, the threat they pose to fish and plants is negligible. Tapwater conditioner, which is based around sodium thiosulphate, is an example of this sort of thing, and let’s face it, since it’s used to make tap water safer for aquarium fish and plants, there’s no reason to imagine it does any harm to fish and plants in the wild.
Put another way, anything you’d put into the aquarium, and then flush out with a water change, isn’t going to be any more dangerous if you just pour it down the drain straight from the bottle. By the time it hits the sewerage system, the difference in con
