I have just rescued a 70 litre fish tank with about 40 guppies in it.

The water is so brown that you can't see the fish and it smells really bad.

When we picked it up we removed 80% of the water to transport it and replaced it with fresh water. After this 80% water change you can still only see about 5cm into the tank.

It has a gravel substrate which is full of detritus. We haven't gravel siphoned yet for fear of sucking up fish which we can't see due to the brown water.

We have also taken out one dead fish, there could be more dead fish in there which we just can't see.

We havn't done a water test yet, due to the color of the water making it hard to read the color in the test tubes. So we have no idea what the water parameters are. But I'm guessing they are way off the charts.

I'm worried that by changing to much of the water two quickly will stress the fish. These fish have obviously gotten used to very extreme water conditions.

How should I go about recovering this thank without harming the fish.

4 Answers 4


Is there a filter in it? If not, add one and fill it with a lot of fine filter cotton. That should be able to catch most of the floating fine dirt.

I would definitely try to siphon the gravel. Keep it close the the gravel (and even stick it in it) & close to the sides, and then you don't have to worry about sucking fish up. Guppies are rater big anyway.
If the gravel is fine, you might also be able to siphon the gravel itself up.
Just stick the siphon in it, all the way to the bottom. Rinse the gravel with clear water, and place it back.

Replacing 80% water initially was a good move. But this is indeed not something you can do everyday because of the fish. But you can try to replace a little water every 2 or 3 days (e.g. 5-10 liters).


When I purchased my tank with no prior experience at all, I had no idea of vacuuming gravel. three months in to it I was out for a month and asked a friend to check on them every couple of days. When I came back my tank was in same condition as yours. I immediately drained almost 70% of the water. Two days later i drained 40% and another two days later another 40% (vacuuming everytime). By this time everything was under control except nitrite. Which took another two rounds of 25% drain every week. Or you can drain 100% of water with vacuuming gravel and find a local treated water supplier to use in your tank. They do get pricey but worth it if you want to save your tank.


So, 70 litres is 18.5 gallons. 40 guppies is a ton of fish for a tank that size. Are you able to separate them between two tanks? If you take the water and fish, split between two tanks and top off with properly conditioned water, this would be a huge start. If not, find homes or pet store to take some? If you don't remove some of the fish, yucky water could remain an ongoing problem - ammonia shock, nitrite and nitrate spikes would result.

For products I'd say get a gravel vacuum, water conditioner for all these water changes, some freshwater aquarium salt (helps kill some bacteria and aids in fin reproduction and ailments, adds electrolytes to water) and lastly, a beneficial live bacteria like API StressZyme or Seachem Stability, just to name a couple. You're losing beneficial bacteria properties as well as the bad when you do water changes.

  • Actually once the water was clear enough to see we found there was closer to 70 guppies. We have removed a lot of them into other tanks and sold some so we have about 20 left. Water conditioner is not required here because our water is not chlorinated.
    – trampster
    Commented May 19, 2017 at 4:58

I will prefer changing the water as early as possible. Siphon out the water and don't worry as fish will move out during siphon. Use some stress coats available in local pet stores after the water change. Using stress coat will help them relieve from stress. Leaving the fish in that water condition will actually deteriorate their health, so better to move them than leaving them in that water. Doing a complete water change just like a new aquarium is a better option. Fishes will thank you a lot for helping them out of that murky water.

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