Chloramine blocking your tank cycle? Fix it

Chloramine in tap water is a really common hidden reason why fishless cycles stall — and it's frustrating because you're doing everything else right. Standard dechlorinators break the chlorine-ammonia bond but leave both behind, and that residual chloramine can suppress the very bacteria you're trying to grow. Before I help you fix it, tell me: what size tank are you cycling, how are you dosing ammonia, and which dechlorinator have you been using so far?

Good news: your cycle is genuinely progressing — nitrite and nitrate showing up means your ammonia-oxidising bacteria are established. The problem is almost certainly your dechlorinator. API Tap Water Conditioner neutralises chlorine but does not detoxify chloramine properly. In a chloramine-treated supply, you need a product that detoxifies the whole compound — chlorine, the chloramine bond, and the resulting ammonia — without adding anything that confuses your test readings. What does your water company say about chloramine treatment, and are you doing large water changes during the cycle?

That explains it perfectly. Every water change you do with that conditioner is reintroducing a chloramine load that temporarily stresses your bacterial colony and adds a small ammonia reading on top of your dosed ammonia — so your readings never quite bottom out. The fix is straightforward: switch to Seachem Prime. It's the go-to conditioner for chloramine tap water because it simultaneously neutralises chlorine, breaks the chloramine bond, and detoxifies the resulting free ammonia into a non-toxic form that your bacteria can still consume. It also temporarily detoxifies nitrite, which gives you a small buffer of protection when you do eventually add fish. Dose it at 1ml per 10 litres on every water change and when you top up. Once you make the switch, most people see their ammonia hit zero within a few days.

Yes, but only with certain kits — and it's easy to manage. Seachem Prime can cause the API ammonia test (which uses Nessler reagent) to read falsely high for about 24 hours after dosing, because it temporarily detoxifies ammonia into ammonium, which still registers. The API test cannot distinguish between the two. If you want an accurate reading after a Prime dose, wait 24 hours or switch to a salicylate-based test like the Salifert or Seachem AmGuard test — those read ammonia and ammonium separately. For your purposes during the cycle, just test before your water changes rather than after, and you'll get a clean picture of where things actually stand.

Exactly right. Switch to Seachem Prime for all tap water treatment going forward, keep your ammonia dose consistent at 2ppm, and only do water changes if ammonia or nitrite spike above 4ppm — which at this stage they probably won't. Your cycle is close. Once you can add 2ppm ammonia and both ammonia and nitrite are back to zero within 24 hours, you're done. You've built good habits with the Dr Tim's ammonia approach — this one product swap should be all it takes to get you over the line.