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New goldfish tank advice


AC Members

Just signed up to the forum, and new to fish keeping in general.
(Apologies in advance for a long first post!)

Unexpectedly, my 5 y/o son got goldfish from his uncle for Christmas. And having spent over a week myself, reading and watching every bit of aquarium/goldfish information that I can find online, in an effort to understand how to look after them correctly.... I can see some issues with our current setup, and would be very appreciative of some advice from the veteran aquarium owners here.

So what he received is:
  • An aquarium 50 x 25 x 30cm, which holds 30-32 litres (~8 US gallons)
  • Lid with a strip of LED's
  • An internal filter (Marina i110), which I believe will turn over enough water per hour for that tank... I will get to issues/q's about the filter later!
  • Some blue coloured gravel
  • 2 artificial plants
  • And of course, fish. 4 goldfish, which I believe are common goldfish, and are around 2.5 - 3" long
Size of the tank
So, going by everything I have read so far, the tank, is eventually, (if not already) going to be too small for 4 goldfish. What would be the advice here? Would getting a larger tank in a couple of years be ok?... or would it be needed sooner? I would probably be looking at 100 - 120 litre tank then (26 - 32 US Gal).

Water conditions
I want to do everything I can to give to fish the best water conditions... but I don't think it's had the best start!
I only saw the tank for the first time about 6 days after they had been brought to our house. I don't the the pet-shop where they were purchased, were knowledgeable at all!
The filter was not even in the tank at this stage, and the water was starting to look dirty and cloudy. The pet-shop had said to his uncle, "you can turn on the filter for a few hours a day if you want"!!
We put the filter in, and then I started frantically googling the best course of action. The water cleared up with the filter running constantly since, and I've done a (~25%-30%) water change since then.
At least the pet-shop did give him fluval water conditioner, (which I used again for the water change).

So there was of course, no tank cycling, no filter running before the fish were put in the tank, (or for their first few days in the tank), and I presume the gravel wasn't washed. I hope it hasn't all affected the fish too much, and we can improve and maintain good water conditions for them.

As I mentioned, the filter was not installed until well after the fish were in the tank. So after it is installed, I'm not sure how long it would take to established a good colony of bacteria? I am thinking of getting 'biological enhancer', to pour into the filter.... a good idea?, or necessary or not?
When I did the water change, I took out the filter, and put it in the bucket of tank water, and gently rinsed the cartridge and bioscreen it the tank water.

The manual says to replace the filter cartridge every 4 weeks or so. I presume that will mean a brand new cartridge will have no bacteria, and will need to build up a new colony again? There is also a 'bioscreen' in the filter, will I presume will keep bacteria, and will not need to be changed?

On the filter throughput... it says on the box up to 100l, which I presume is for tanks up to 100l... and not 100l p/h? The booklet does seem to say 380l/h, which would be over 10x our tank.

I have ordered the following already: Siphon/gravel cleaner, magnetic tank cleaner, replacement filter cartridges, hollow log decoration, stick on thermometer, and some more food, (tetra goldfish granules, are what we have already).
I'm also thinking of an air stone and pump, if the filter isn't aerating the tank enough. Testing kits, biological enhancer, and possibly some more decorations, (but don't want to fill u the tank too much).
Any thoughts on this list, and other items that we might need?

Any other advice, tips, or insights that could help us in looking after, and enjoying these fish , would be very much appreciated.



AC Members

As your research has indicated, an 8 g tank is far to small for a goldfish. A 26-32g tank is also far to small. Common and comet gold fish really shouldnt be kept in aquariums as they grow to
large. They will become stunted rather quickly and belong in ponds.

Read the sticky on fresh water aquarium cycling. Nitrogen cycle is very important. Gold fish are incredibly dirty fish and you will have a very hardtime keeping good water quality for them in such a small tank. You will need to do daily water changes while your cycle establishes itself.

Make sure you get an API fresh water master test kit. Liquid only, strips arent very accurate.

Personally, I would highly recommend returning the goldies or rehomimg to a pond. Get your son a betta or something more suited to your tank size after youve cycled it.


No freelancing!
Agreed--returning the goldies and getting something appropriate for the tank will be best. A bigger tank in general will be easier, but for goldfish, you'd be looking at a 55 even in the short term.

For the time being, water changes daily, and don't discard the filter media. Yes, the instructions say to do that, but they want to sell you stuff. Rinse it off as needed to keep water flowing, otherwise no reason to replace it.

Good luck. You might want to look around for a local fish club--most have monthly meetings, and can help you rehome the goldfish, plus find something interesting and appropriate to keep instead.


AC Members
Thanks for the replies.
It’s kind of what I expected, after researching their requirements.... but not really what I wanted to hear!

It is a bit of a quandary then, (and I wish general pet shops had any bit of knowledge, not to sell completely inappropriate pairings of tanks and fish!). But my son is pretty attached to them now, and he would probably be devastated if they were returned!. They are named and everything, you know.

So we’ll have to figure out what to do.... save up for a large tank, or dig out and create a pond!
Or just try and talk to him, and say it’s not nice for the fish in there, and they won’t be happy in it.

I’ve attached a photo of them, just to confirm they are common goldfish, (I’m pretty sure, but just to be 100%)

How long would be alright at their current size, to have them in a tank that size?
Would it be considered cruel?, or unhealthy for them? If we do our best with the water. (I must get a testing kit).

the loach

AC Members
Take a look at this link:

I would just explain his uncle made a mistake, return the goldfish and get some rosy barbs for him:

These are pretty much the fish you hoped the goldfish would be. They won't get big even though 8 gal is too small for most fish, you could keep a number of them comfortably in a 20 gal. Like goldfish there are several varieties such as fancy tailed ones:

Alternatively you could get golden barbs as they stay even smaller as rosy barbs.

There are quite a lot of fish easy to maintain in small tanks but not goldfish.


Global Moderator
Staff member
Andy, those are really nice looking comets/commons. They might be sarasa comets.

Like said 4 of them in 8 gallons will not be manageable.

If keeping goldfish is a must for you, keeping two fancy/fantails in a standard 29g is manageable in my opinion, but again, not ideal.


AC Members
Yeah, the 8 gallon tank is WAY too small. Get a tank at the next Perco dollar per gallon sale, but I'm not sure when the next one is. I think the true "dollar per gallon" deal only goes up to 29 gallons now, but I was able to get a 55 gallon tank for $75 at the last sale, which is still a substantial discount. If the next sale isn't soon enough, look on Craiglist for a tank. Those fish will die soon if you don't get them into a larger tank.


AC Members
Thanks for all the replies guys.
Sorry I haven't responded in ages.... I was waiting until I had some news about a tank.
I have been looking at getting a larger tank, as opposed to bringing them back to the pet shop.
We're all kind of attached to the little guys!, and I do like the idea of having a nice big tank to enjoy.

I was looking at 2nd hand tanks, and hoping to get something like a 450L (120gal) tank. There was a Juwel Vision 450 for sale with a brand new Fluval fx6 for €650.... but even at that my other half said the tank and price was too much. It was a great deal though, and there was also a 6ft clearseal tank with cabinet and two Eheim external filters for €650 also.

But we've gone a bit smaller, and hopefully big enough for the interim, (we may upgrade again hopefully).
I found a great condition Fluval Roma 200L (55gal), for €180, and they'll take €150 for it. I'll pick it up tonight, and see exactly what it's like then.
I believe the filter in them is a Fluval U4, which is meant to be a decent internal filter. I'll see what it's like on it's own, and may get an external filter again.

Thanks for the link, the loach, It's a good resource.
Freshyfresh, They look like they probably are sarasa comets. I was looking them up.
Carpcharacin, we wouldn't get deals like that here. There are some custom tank builders around, but you're paying custom made prices then.

So my questions for the new tank are:

The tank comes with gravel and decorations, so I'm wondering should I fill it with water, leaving them in place, and cycle the tank like that?...
Or give the gravel, and decorations a good clean, before filling the tank and cycling it?
I have got some fluval cycle to help start it cycling.

Also, when it comes time to add the fish once the tank is cycled, should I do them one at a time?, or all together?
I would get them into a bag, (or separate bags?), and acclimatise them by floating the bag(s), in the new tank, and then netting them into it, after the temperature has balanced?
I would probably add small amounts of the new tank water into the bag, bit by bit first, before getting them into the new tank.

I'm not sure how long they have the tank emptied, but I presume would all the bacteria in the filter be dead?
If I start it up again, with the same media, will it be easier to get new bacteria growing?, or would I be better to replace the media, (or just sponges) in the filter, to start over new?

Thanks again guys


Global Moderator
Staff member
Welcome back!

Never fails, when you're in the need for a tank, there's not a deal to be had!

It doesn't sound like the beneficial bacteria in the tank you are buying will be viable. The gravel, decor and filter media would have to stay in tank water the whole time.

In terms of establishing a new cycle, be prepared for lots of water changes, get a good dechlorinator/water treatment product that neutralizes chlorine/chloramine and ammonia.

A water parameter test kit that can measure for ammonia, nitrite and nitrate in PPM is a must also.


AC Members
Yeah the tank has been empty of water for a while now.
The gravel and decor are still in it, so that's what I was wondering, should I take it all out and clean it, and wipe down the inside of the tank?
Or just fill the tank again, and treat the water, add the fluval cycle as directed, and start it cycling?