Ammonia smell from canister filter

[uklau]

Hi, I was doing WC this morning a little bit different than what I used to do. I switch off my canister filter & continue with the prunning & cleaning. About half an hour later, I started to drain out the water through the filter outlet. I can smell ammonia for the first 2-3 minutes when the water started to flow out. I believe the problem comes from the canister filter as I didn't smell any ammonia from the surface of the water.

No fish is dying & plants are doing well (except some BBA due to CO2 circulation issue). I use Nutrafin beneficial bacteria weekly, after water change. Any thoughts? Thanks.

[grey_fox]

Probably dead plant/deritus material from your canister. Keep a portion of your tank's water, dump away the water in your canister and fill it back with the kept water into the canister.

[uklau]

Thanks, greyfox.

I've found the root cause. I have a T connector connected to the inlet of the external filter. This allows me to drain water from tank. The water that remains in this part of the tubing is causing the smell. I guess that's the part where the water remains static (not flowing into the filter).