My goldfish was showing signs of illness, then started shredding its tail and losing its colour - I did a complete water change and cleaned the filter and tank/gravel. I purchased some Tri-Sulfa tablets. Once I added these into the tank, the fish sunk to the bottom and displayed very little movement - after 20 minutes it did two large, thick poos. Is this normal?

  • When you say you 'cleaned the filter and tank/gravel' can you explain exactly how you did this? That's an important detail.
    – Henders
    Commented Mar 18, 2019 at 11:33
  • With hot water.. I let the hot water run through the filter until water was clean.. and removed all gravel and did the same.
    – Nejla
    Commented Mar 18, 2019 at 12:53

1 Answer 1


Treat the fish for Ammonia poisoning

If it's been any length of time since you took all the gravel, filter, water out and replaced them, you need to do two things:

  1. Check the ammonia levels in your tank
  2. Treat the tank if the ammonia levels are high

What's happened?

By washing your filter and gravel in hot water, the chances are you've killed all of the beneficial bacteria that live in the substrate (gravel) and the filter (in the sponges / filter media) which means that there is nothing left to convert ammonia into nitrite and nitrate. You'll probably want to learn about the nitrogen cycle here (video).

Your fish may have been suffering from ammonia poisoning to start with. Remember that any amount of ammonia in the water is potentially lethal to fish. You should avoid doing 100% water changes because it is normally not necessary and if the parameters of the water has changed at all then your fish will have to adapt to it very quickly which can be stressful. There's a lot of debate about how much water you should change but normally it is somewhere between 20 - 40% per week.

What now?

  • Check your water parameters with a test kit
  • Consider changing your maintenance routine.
  • Add some 'quick start' aquarium products to boost the beneficial bacteria levels in the tank.
  • Be very careful removing all the gravel or filter material because these contain the bacteria which is the life blood of the aquarium.
  • Are giant poos symptomatic of ammonia poisoning? My tank maintenance isn’t perfect but after 30% water changes my goldfish always upset me by producing big poos. My filter and gravel are left dirty enough to be healthy. I’d always assumed it was a sort of osmosis, but is it ammonia poisoning?
    – Pam
    Commented Apr 8, 2019 at 21:23
  • @Pam - I've normally associate no poo or stringy white poo with ammonia poisoning. If you're at all worried about ammonia, grab a test kit and check it. It's worth the $30 for the amount of fish you've got sat in your tank. You can join us in the chatroom to chat about fish if you fancy! :D
    – Henders
    Commented Apr 8, 2019 at 22:02

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