Neglected goldfish. I am a novice fish owner.

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FishieFishy

Aquarium Advice Newbie
Joined
May 18, 2025
Messages
7
Location
Ireland
I received a pair of, I think both are, sarasa comet goldfish. And I presume they both are male because of the tubercles on the operculum.

1. How likely are the goldfish going to be growth stunted forever if they were kept in a 20 liter (5 gallon) aquarium with a tad more than half of the water filled in it for more than three years of their lives?

They were only barely fed a sprinkle flakes and pellets every second day and when the former owner left for vacation they didn't have the filter on for at least 5 days. Said filter (I think HOB?) is very defective now - barely, if at all, does it blow bubbles and I have to constantly adjust it for it to work properly every few hours.

The goldfish have never had an airstone with the former owner, which makes me wonder how they didn't suffocate to death. Goldfish are both less than 10 cm long if I disregard their fancy tail, otherwise a bit less than 15 cm.


2. From the past few weeks I got them, I have been feeding them boiled vegetables (peas, broccoli, green beans, cauliflower, asparagus), raw cucumber, a bit of coconut, buckwheat, couscous, egg yolk, bloodworms, tiny brine shrimp. Are these ok to feed? That is, I found no information online regarding feeding coconut or buckwheat, quinoa, oats and other cereals to goldfish. Can I feed them cooked lentils and all types of common store bought cooked beans, chickpeas? Can I feed a pancake made out of potatoes and some milk in it? A pancake made out of curd? Very yeasty, full of seed expensive bread - maybe soaking or cooking the bread for the fish? I plan on buying them seaweed and edible marine plants like, maybe, duckweed soon. I read online I should prioritise vegetables.

I am not sure how much information I shared is at all relevant. I am definitely upgrading the tank to at least 360 liters in a few weeks time, in case anyone asks, or cares.
 
If the goldfish have been in 10 litres of water for 3 years they have done exceptionally well. For context though, the confirmed world record longest lifespan goldfish is 43 years, looking at the bowl it was kept in its in the region of 20 litres, and that fishes tankmate also lived nearly 20 years. But that's not normal, they will have otherwise looked after the fish very well, and basically won the lottery twice with fish health, genetics etc.

10cm at 3 years is quite stunted, and I don't see them recovering to full sized adult size, but the bigger aquarium will improve conditions and you could see the fish put on some size. The historic conditions may also shorten their lifespan, but people do win the lottery every week.

What you want sure you don't do is change things too suddenly. Fish don't do well with changing water conditions. Slowly improve conditions in their small aquarium, smaller more frequent water changes to start with rather than bigger ones. I would fully cycle the bigger aquarium before moving the fish, which could take a couple of months. Do you know how to do a fishless cycle?

I'm not really a goldfish person, but your food sounds like a good varied diet. I would do the starchy foods and cereals as an occasional thing rather than a staple.

Do you have a good test kit? What sort of water change schedule are you maintaining in the smaller tank?

There are no guarantees here, 3 years in such poor conditions will have had a lasting impact on the fishes health. Regardless of what you do they could live years or weeks. But you improve the chances of a long and healthy life by improving the living conditions.
 
I only have a ProAqua JBL test strip I bought in a haste, which doesn't measure ammonia, otherwise all of the paramaters it measured were fine and stable. The former owner, from what I gather, has never tested the water for 3+ years.

I don't have a set schedule, but I think I change about 5% ish water per day.I primarily put more water in than change it currently. Like you said, I am trying to be careful to not overwhelm the fish.

I am still trying to figure out the dimensions of my aquarium and whether I want it to have low iron glass or go for cheaper and be more scratch resistant but have a more green/blue tint glass. I didn't do enough research of what substrate for a plant filled tank I should strive for let alone how to cycle a fishless tank.

The goldfish look very lively and active, especially when begging for food. Is that deceptive? Their stool has these transparent stringy thin strings hanging from them, but have now started to look more solid brown.
 
People typically work on 120 litres for one comet goldfish and 40 additional litres per additional goldfish as a minumum. That's minimum, and is going to provide some quality of life, but not really going to be ideal. The 300+ litre size you mention is going to be much better than the minimum a lot of people work from.

You also need to consider that goldfish are very messy fish and need a lot of filtration. So look at something rated up to double your aquarium size. Something like a fluval 407 is rated upto 500 litres, and would do a good job on the 300 litre aquarium you suggest.

The 5% water change per day is a good starting point, but I'd gradually work up to about 30% per day. On the larger aquarium, with a couple of goldfish you might want to be doing 50% once per week, or 30% twice per week.

What water parameters is your test kit showing?

I would look for a liquid test kit, like the API Freshwater Master Testkit. It covers what you need to monitor water quality and cycle an aquarium. pH, ammonia, nitrite and nitrate. Is fairly easy to use. Is accurate enough for what you need. And gives you 100s of tests for your money.

Once you are comfortable with your water chemistry you won't test so often. It's at least a couple of years since I tested water on an established aquarium, but you want a test kit while cycling and it's always a good thing to be able to test your water if you think something is off.

Goldfish don't have much in the way of a digestive system. Food just goes in one end and straight out the other. They don't really have a stomach to hold food. As such they are always hungry, and should be fed several times a day, little and often. I don't know how much you are feeding now, or how much their previous owners fed, but be careful with feeding in the small aquarium as food produces waste, and waste leads to poor water quality, and in a small volume of water that water quality will more quickly become toxic.

Goldfish will eat the plants. While I understand that it is your intension for the fish to do this, don't expect a spectacular planted aquarium because the fish will work against you there. So I wouldn't put too much effort into the planting.

Sand is generally considered safer for goldfish than gravel, and sand will be fine for low nutrient demand, easy plants. But the goldfish will likely uproot anything you plant in the substrate, so you will have to see how that goes if you try rooted plants. Floating plants, and rhyzome plants like java fern and anubias might be easier to manage.

Here is my guide to a fishless cycle. I also did a fish in guide should you decide to move the fish into their larger home as soon as you set it up.

 
Test strip:

Nitrate ~10 ppm

Nitrite <2 ppm

GH >125 ppm

KH there is a colour discrepancy, so I am always confused by the result. Maybe ~107 ppm

pH 7.6

Chlorine 0



After about 10 minutes the reading changed to: nitrate 0 ppm, nitrite 2 ppm and ph to 8.0. I am not sure if the test strip is still valid at this point.



i will check out the 407 fluvial and the testkit.



I overfeed my goldfish by a lot, actually. They were skinny for a goldfish when I got them. I know I should discourage myself, but very hard to resist the begging.



30% a day seems a bit too much for water change. I get there can be builtup toxins, but what about disrupting and lowering all of the beneficial bacteria at this huge rate. Am I overestimating it?



I am still kind of sad that the goldfish lives are going to be contained in the 363 liter aquarium for, maybe, the rest of their lives. I wish I understood them better.
 
The microbes that are responsible for the nitrogen cycle don't inhabit the water column. They live on surfaces where there is a good flow of oxygenated water. This will be on your substrate, on your aquascape, on the glass your aquarium is made from, but mostly on the filter media in your filter. Doing water changes has a negligible effect on your cycle. I'm not saying you should immediately go from 5% per day to 30% per day, I'm saying do 5% today, and 10% tomorrow, then 15% the next day, until you are changing 30% every day.

While water changes can be stressful, and bigger water changes can cause swings in water parameters if your tap water is significantly different to what's in the tank, it's better than living in toxic water. In situations where you are concerned about water parameters swings then smaller more frequent water changes are better than bigger less frequent ones. 5% water changes are hardly worth doing. Your 2ppm of nitrite will be reduced to 1.9ppm with negligible improvement in water quality. A 30% water change isn't huge, 30 to 50% water changes are pretty standard.

Your water parameters are very concerning. 2ppm nitrite is simply to much and will be causing an issue with the fishes ability to extract oxygen from the water. You really need that down below 0.5ppm. Based on it being 2ppm, that would be 2 x back to back 50% water changes.

It's something that that the fish has probably been living in for some time though, and to give some comfort nitrite toxicity is lower at higher pH levels, which is probably what's keeping the fish alive. I would certainly be working towards changing a larger amount of water until you get your bigger aquarium. We also have no idea on ammonia levels, which is more toxic at higher pH.

As the small aquarium is fairly established, its likely that the aquarium size and filtration is simply insufficient to cycle being so overstocked. With that in mind, I would get the larger aquarium ASAP and move the fish over ASAP as well. Do a fish in cycle rather than fishless. Make sure you do a good acclimation process before moving them over. They are better off in a larger uncycled aquarium than a smaller uncycled aquarium.

As for your test showing a different result after a few minutes, do the test as directed on the test kit instructions. If it says read the test immediately, read it immediately. If it says read the test after 30 seconds, read it after 30 seconds. If it says read the test after 2 minutes, read it after 2 minutes.

Goldfish, particularly comets are better off outside in a pond. After 3 years in an aquarium a pond would probably be very stressful for them, so a bigger aquarium is the best route.
 
I am still aversive towards doing 30% water changes soon, especially when the former owner has changed their water once every 1 or 3 months. But the goldfish seem to acclimate very easily, if I am not deceiving myself. I will take the nitrites more seriously.

And thank you for taking the time to write all of this, genuinely.
 
I am still aversive towards doing 30% water changes soon, especially when the former owner has changed their water once every 1 or 3 months. But the goldfish seem to acclimate very easily, if I am not deceiving myself. I will take the nitrites more seriously.

And thank you for taking the time to write all of this, genuinely.

Just because someone does something wrong all there life does not make it justifiable.
From Aiken post #2
Slowly improve conditions in their small aquarium, smaller more frequent water changes to start with rather than bigger ones
From Aiken post #7
I'm not saying you should immediately go from 5% per day to 30% per day, I'm saying do 5% today, and 10% tomorrow, then 15% the next day, until you are changing 30% every day.
If Aiken tells you something about fish you can take it to the bank. There are only about 3 to5 people on this site I can say this about.
Talking about people doing the wrong thing for a long time and getting away with it
In a unrelated but true story. I found out about a man who drove home most of his adult life after drinking to much. Never had any tickets always got home safe never hurt anyone. Until one morning he crossed over the center line then hit my mother head on and killed her.
 
The 1 per month changes comment was supposed to mean I do not want to make too sudden changes so soon. It was not a justification for primarily changing little water in of itself. I guess I had to spell it out.
 
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