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Water Conditioner: What It Removes and Why Tap Water Needs It
Older aquarium books told you to let tap water stand overnight before adding it to a tank. That advice was written when municipal supplies were treated with chlorine alone, which gasses off. Most systems now use chloramine — chlorine bonded to ammonia — and chloramine does not gas off. It will sit in a bucket for a week and still kill your filter bacteria.
What is in tap water
Chlorine
A disinfectant, and effective enough that it does the same job on the nitrifying bacteria in your filter as it does on pathogens in the pipe. It is also directly damaging to fish gills.
Chloramine
More stable than chlorine, which is why it is used: it survives all the way to the tap. That stability is the problem. It does not evaporate, and when a conditioner breaks the bond it releases free ammonia, which is why a good conditioner also neutralises ammonia rather than simply dechlorinating.
Heavy metals
Copper from plumbing is the common one, and it is particularly hard on invertebrates. Shrimp and snails will show stress at concentrations fish tolerate. Conditioners that chelate metals matter far more in a shrimp tank than most people realise.
Choosing a conditioner
Read the label for three things: does it remove chlorine, does it break and neutralise chloramine, and does it bind heavy metals. A product that only dechlorinates is not enough on a chloraminated supply. Anything described as a complete conditioner normally covers all three; our water care listings state what each one handles.
Concentration varies enormously between products. Some dose a capful per ten gallons, others a few drops. Always dose by the label rather than by habit carried over from a different bottle.
Dosing for a water change versus a fill
For a routine water change, you have two options. Treat the new water in the bucket before it goes in — the cleaner method, and the one to use if you are unsure. Or dose the tank for its full volume and add untreated water slowly; that works because the conditioner is already distributed, but only if you dose for the whole tank, not the replacement volume.
For a brand-new fill, dose for the full tank volume and give it fifteen minutes with the filter running before anything living goes in.
Slight overdosing is not harmful with mainstream conditioners; underdosing is. If you are estimating, estimate high.
Temperature matters as much as chemistry
Conditioned water straight from a cold tap is still a shock. Match replacement water to within a couple of degrees of the tank before adding it. In practice that means mixing hot and cold at the tap and checking with a thermometer, not guessing by hand.
Rapid temperature swings are one of the more common triggers for ich, and they are entirely avoidable.
What conditioner does not do
It does not remove nitrate, which is what water changes are for. It does not fix pH or hardness. It does not substitute for cycling a tank. And it does not detoxify ammonia indefinitely — products that bind ammonia hold it in a less toxic form for roughly 24 to 48 hours, which buys time in an emergency but is not a filter.
A simple water change routine
- Siphon 20 to 30 per cent, vacuuming a different section of substrate each week rather than the whole floor at once.
- Mix replacement water to temperature.
- Add conditioner to the bucket at the labelled rate.
- Pour back slowly, onto a plate or your hand, to avoid stirring up the substrate.
Weekly for most tanks, fortnightly for a lightly stocked and well-planted one. More frequent small changes beat occasional large ones, because they keep parameters stable rather than swinging them.
If you use a well or an RO unit
Well water usually needs no dechlorinator, but it may carry iron, high hardness or dissolved gases, and it is worth testing before assuming it is fine. RO water is the opposite problem: it is stripped of everything, including the minerals fish need, and must be remineralised before use. Neither case is unusual out here and neither is difficult once you know which one you are dealing with.
Storing and handling it
Conditioner keeps for years in a closed bottle at room temperature, but it degrades faster in heat and sunlight, so the shelf above a radiator or a windowsill is the wrong place. Some formulations develop a sulphurous smell as they age; that smell is a sign the product is past its best rather than a normal characteristic, and a fresh bottle is cheap insurance.
Measure with a cap or a syringe rather than pouring by eye. The concentrated products are concentrated enough that a generous splash into a small tank is a genuinely different dose from the one on the label, and it is easy to do without noticing.
Municipal supply changes catch people out
Water utilities periodically switch treatment method, and they often run a temporary free-chlorine flush — usually in spring — during which chlorine levels are markedly higher than normal for a few weeks. Tanks that had been running fine on a light dose can suddenly show stressed fish and a filter that seems to have lost ground.
If several tanks in the same neighbourhood have an unexplained bad fortnight at the same time of year, this is usually why. The response is simple: dose conditioner at the upper end of the label range during a flush period, and hold off on filter maintenance until it is over.
Keeping it simple
One complete conditioner, dosed by the label, used every time water enters the tank. That is the whole discipline. Everything on our water care page states what it treats, and if you are unsure what your supply contains, ask us — we have been servicing tanks in this area long enough to know what comes out of the tap. Shipping details are on the shipping policy page and the full range is on the shop page.
From our shelves
Products in this store that relate to what is covered above:
Prices are in US dollars. Delivery timings are on our shipping policy page and the return and refund policy sets out the window if something is not right.
