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Old 01-26-2021, 10:00 PM   #1
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Comet goldfish very lethargic

Need some help to bring back my fish to good health. But I fear it might be too late. Any help/advice will be much appreciated. Thanks in advance.


We have 2 comet goldfish. One is about 4cm (1.5 inches) and the other about 6cm (2.4 inches). They are in a 28L (7.4 gallon)tank. The big fish is a lot bigger in size as its more rounded even though its not that much bigger in length. It seems since we bought them the big one has been getting bigger and bigger but the small one is growing a lot slower.

The tank has a filter and an aeration stone.

They eat flakes. The flakes we feed them are quite big, so now I crush them into tiny pieces.


GH 120 (ideal),

KH 80 (caution to ideal)

pH 6.0-6.5 (danger to caution)

NO2 0-0.5 (ideal to caution)

NO3 40 (ideal)

NH3/NH4 0 (ideal)

Water temperature 24.3 degrees Celsius (75.7 degrees Fahrenheit)


We bought the fish about 5 months ago and have had no issues with them until about 6 weeks ago. Even after two 50% water changes and one full tank water change. It all started after we did our 2nd full tank water change - see below

They have been fine up until 6 weeks ago, when I changed all the water and washed the gravel. At around the same time we also bought a different brand of flake food.

Since then they have been acting really strange:

1. They stay mainly at the bottom without moving and hiding inside a rock feature or behind plants.

2. But they also come up and hang in the corners of the tank almost vertical (75 degrees), like sucking for air.

3. At times they swim fast and erratically (for about 10 seconds at a time), almost bouncing off the gravel and side of tanks, like some kind of nervous system issue? They don't both do it at the same time, just at different times.

4. We thought the big fish is picking on the small fish but not really. The odd thing is the small one sometimes huddles next to or underneath the big fish at the bottom of the tank

5. Sometimes while they are at the bottom of the tank the small fish will be pecking slowly at the big fish's belly, the big fish will just stay still, it wont try and swim away.

6. They both come up to eat when fed, but it seems the small fish is up their looking for food but hardly eats them but it keeps looking for them and swims past them as the flakes are floating, occasionally it will eat a small piece here and there.

7. Initially the big fish was very lethargic, and the small one was fine, then the small fish was lethargic and the big one was fine. But now both of them are lethargic but the small fish is in a worse condition

8. Sometimes they hang almost vertical facing down at the aerator bubbles, trying to get oxygen from the bubbles. Often they will hang by the filter exit where the water is being pumped back into the tank.


1. Lets say today is week 6

2. Week 1 I changed all the water and washed the gravel. I put in the normal stress coat and stress enzyme droplet. Around this time a week later maybe, we bought new flake food (bigger flakes). I moved the fish to a large bowl while I took the gravel out to clean. I realize now, this wasn't a good idea and should have just done a 50% water change.

3. Week 2 we noticed the large fish was lethargic

3. Week 3 we noticed both fish were lethargic.

4. Week 3 we did all the tests but ammonia, and everything came out fine. We fed the fish a pea each (crushed without skin), just in case they were constipated and we reduced the amount of food. As we were overfeeding them big time. We changed 50% of the water.. We also started putting 5ml of API melafix into the tank for the next 7 days.

5. Week 4 the big fish seems a bit better but the small fish is lethargic still. It gills are more exposed and its like its face has shrunk and its malnourished. We did a ammonia test and it was at zero.

6. Week 5 both fish are very lethargic, hardly moving and hanging at the bottom without moving. Only coming up for food. The small fish hardly eats. And its not like its being bullied by the big fish.

7 Week 6 The small fish swims occasionally but otherwise it tries to hide right up inside the top of the rock feature or stays up the top in the corners. It will swim occasionally and still comes up for food but hardly eats. Both still do that erratic swims (bouncing off things) a few times a day - Mainly the big fish

NOW (week 6, yesterday): I have moved the small fish into a big bowl with new water and some rocks for cover. I treated the water with Stress coat, stress enzyme droplets and put in the API melafix as well. The water is aerated. I gave it another crushed pea but didn't eat really, it ate a few tiny flakes of fish food. It just looks really sick or malnourished. Both fish seem to be pooing ok. The big one is in the tank just hanging up with its mouth at the top of the water at almost a75 degrees angle (close to vertical) - It still eats ok as normal, no issues, but hardly swims unless its feeding time.


1. We thought the water was in bad condition but it seems ok, apart from the pH reading at week 6 (yesterday), which seems to be a bit low.

2. We thought they were constipated so we reduced feeding and gave them some peas.

3. We though the small fish was being bullied on by the big fish, but it doesn't appear to be so.

4. Could be some bacterial or fungal infection?

5. Is it something in the tank, hard to tell if the small fish in the bowl is getting better or not as its only been there for 12 hours now.

6. Is it the water temperature as its mid summer here and in the last 5 weeks the air temp inside the house is about 25 degrees during the hottest part of the day

7. Is the small fish just so malnourished as it hasn't really eat for 5 weeks since we got the new fish food with the bigger flakes? And now its so sick it cant even eat?

8. Its likely the fish were slowly getting sick even before we did the water change or bought the big flakes - Maybe the water change made it worse.

Thank you

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Old 01-27-2021, 02:46 AM   #2
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A 28 litre tank is nowhere near big enough for 2 goldfish. A single goldfish needs about 120 litres with an additional 40 litres for each additional goldfish. They are also very messy and need filtration for double the tank size.

What is happening is they don't have space to grow. Goldfish typically grow to about 12" length and will live to upto 20 years. Without space their bodies stop growing but their internal organs dont. Their bodies will be stunted, they will be in poor health, and they wont live their full life.

Goldfish are also temperate and dont need a heated tank. 24c is too warm for them. Their metabolism is increased at higher temperatures and oxygen content in the water reduces as temperature rises. They would be happier at normal room temperature. There are ways of cooling tanks when air temperature gets too high. Lots of surface agitation to increase oxygen content, turn off lights, run a fan over the water surface.

You can treat the fish with medication, but the root cause of your problems is an unsuitable living environment and nothing will improve unless you provide one. Get a bigger tank and hope your fish can recover.

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Old 01-27-2021, 05:26 AM   #3
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Also there should be 0 Nitrite.

The information in the article linked in my signature can help you learn about the nitrification cycle.

If you are using test strips they are frequently inaccurate. I accidentally killed a nearly full tank of fish relying on test strips which had been previously double checked several times with the liquid test kit.

The below thread applies to comet Goldfish as well as they get even larger up to 16-18 inches /43-44cm and can grow very fast in ideal conditions
Favorite tank right now - 12G Edge nano fish

New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?
Start here - Aquarium Advice Article
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