Tank almost killed my goldfish please help

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Aquarium Advice Newbie
Jul 8, 2023
Okay so quick BG: I got my goldfish at a carnival a year ago and I had no idea how to take care of him. The carnival staff tried to sell me a .75 gallon “tank” for him and a packet of food for like $25 which seemed insane to me so I went to my local pet store and they told me I just needed a 3 gallon tank for him so that’s what I got. He lived in that tank for about 11 months as I genuinely didn’t know better (and with another goldfish too for 6 months before the other one passed away). Roughly 2 months ago I FINALLY discovered that he actually needs a bigger tank so while I’m saving up for a bigger tank set up my mom got him a 7 gallon tank that he’s been in for the past month and a half. He has a fully functioning heater, filter, and lighting system in his 7 gallon tank.

Yesterday he got ammonia poisoning and I did a 60% water change in his tank (with preconditioned water from the aquarium store), changed out his filter cartridge, added 2 drops of accuclear, algaefix, stress coat+, and ammolock each and after a few hours he perked up a bit but for the most part nothing changed. He was still paralyzing every few hours for about 2 minutes at a time and started swimming upside down. Once I saw this, last night, I tried a full Hail Mary and put 90% of the preconditioned water and 10% of his tank water into his 3 gallon tank, set the old filter up in it and put him in there. And lucky for me he not only lived but is acting completely normal again (he’s even trying to beg for food again every time I walk by haha)

So I’ve done so much research about tank cycling in the past 15 hours as another redditor told me how important it is to do that. Even after all that research I still feel completely lost since all of the explanations that I’ve found are for new tank set up but he’s already been living in this tank for a month and a half already so would it already have the heathy bacteria it needs? I honestly am just at a loss since I can’t figure out how to make his 7 gallon tank habitable again without killing him. Especially since the 3 gallon tank is supposed to be a temporary solution. Any advice or help would be so so so appreciated I really want what’s best for my fish and am willing do to anything. I’m going to go get an air pump for his tank since a lot of suggestions said to do that but I’m completely hopeless on where to start.


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Sorry to break this to you, but 7 gallons is nowhere near big enough for a goldfish. Really goldfish belong in ponds, but if you really want to keep a goldfish in a tank 30 gallons would be minimum for a single goldfish and filtration rated for 60 gallons.

I can tell you all you want to know about cycling a tank, but its pointless in a 7g tank. Your fish will simply produce too much waste for the filtration to cycle out the harmful waste and sufficiently dilute the less harmful waste your filter cant remove.

Goldfish get big. They can easily get to 12 inches if kept in a suitable environment. They live a long time, again if kept in a suitable environment they live decades. When kept in too small an environment they are just going to be living in their own waste and their growth will stunt. They will live shortened lifes and be more prone to illness and less prone to recover.

If you arent able to give it a suitable home rehoming the fish to someone who can provide a suitable environmental would be best for the fish. If thats not an option then very regular water changes will help. Probably daily would be needed, and even then the fish wont have a good quality of life.

How do you wish to proceed?
Don’t worry I’m saving up for a big tank for him right now. I really just need him to hold on for a few more weeks in the 7 gallon tank until I can afford the 35 gallon tank I’ve been planning on getting. I was wondering if there’s anyone can do to his tank to make it hospitable for just 3 more weeks? Thank you for your help so far <3
It typically takes 6 to 8 weeks to cycle a tank, so its not worth doing this. And as said your fish will simply produce more waste than a cycled 7g can deal with.

As said, you need to compensate with plenty of water changes. Get yourself a test kit. It should test for pH, ammonia, nitrite and nitrate. API Freshwater Master Test Kit is a good one to go for. Test daily, if you detect ammonia or nitrite change 50% of the water. Feed lightly, half as much as you would normally. This will reduce waste in the tank.

Until you can test your water, change 50% of the water daily.

All this will keep your water at non toxic levels. It wont stop stunting due to being in too cramped a space though, but thats probably already happened. A year in a 3g tank wont have been healthy. A year old goldfish should be 5 or 6 inches to give you a guide. So going forward dont expect a 10 year old fully grown fish, but giving your goldfish a suitable home will help no end.

And remember about the filtration. You will need filtration rated for 60 gallons in your 30g+ tank.

Ill post a thorough method for cycling a tank for when you get yoir larger tank. And you will have a couple of tanks to keep some guppies or a betta if you wish.
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To cycle a tank you need to grow denitrifying bacteria to consume ammonia and nitrite that your tank produces. The bacteria needs an ammonia source to grow colonies sufficient in size to consume all the ammonia and resultant nitrite and turn it into nitrate which typically you remove through your regular water changes.

A fish in cycle uses fish waste as an ammonia source and regular water changes are undertaken to ensure that water parameters are maintained at relatively non toxic levels.

Set up your tank. Make sure everything is running smoothly. Make sure you have used a water conditioner product with any tap water you have put in your tank. Seachem Prime is a water conditioner that will also detoxify some ammonia for a day or two, so is a good choice for a water conditioner while cycling a tank with fish.

You should have a test kit. Preferably a liquid test kit. It should test for ammonia, nitrite, and nitrate.

In ideal circumstances you should be starting a fishless cycle with a low bioload (number of fish). 1 small fish per 10 gallons/40 litres is a good number of fish, but this can be tweaked a little for fish that are social and don’t do well on their own. Ideally a hardy type of fish. You may have fully stocked (or overstocked) your tank before you knew about cycling. In these circumstances, if its not possible to return fish, you will have to make the best of it.

If you haven’t already done so, add your fish. Acclimate them to the water in your tank before doing so.

Feed lightly to start with. Daily as much as is eaten in 2 minutes, or as much as is eaten in 3 minutes every 2 days. You can increase to full feedings if you are confident your parameters aren’t getting too elevated too quickly and water changes don’t become a daily thing.

Start to regularly test the water for ammonia and nitrite. At least daily. Depending on your bioload you could start to see ammonia quite quickly. Nitrite will likely take a little longer to appear.

Your target should be to keep ammonia + nitrite combined no higher than 0.5ppm by changing water whenever your water parameters exceed this target. 0.5ppm combined is a level of waste that is sufficient for your cycle to establish but relatively safe for your fish.

If you see 0.5ppm ammonia and 0.0ppm nitrite (0.5ppm combined) then leave things be. If you see 0.5ppm ammonia and 0.25ppm nitrite (0.75ppm combined) then change 1/3 of the water. If you see 0.25ppm ammonia and 0.75ppm nitrite (1.0ppm combined) then change 1/2 the water. If water parameters get worse than these levels it may require multiple daily 50% water changes to maintain safe water conditions. This is more likely to happen with a fully stocked tank.

Remember to add water conditioner whenever you put tap water in the tank.

Over time the frequency of water changes and amount you need to change to maintain your ammonia + nitrite combined target will reduce. You can also start testing for nitrate and should see this rising. If you are finding the ammonia and nitrite in your tests are consistently low, and you aren’t already fully stocked, you can add a few more fish. It may take a few weeks to get to this point.

Once you add a few more fish, continue to regularly test the water and continue to change water if you exceed the 0.5ppm combined ammonia + nitrite target. With added bioload the frequency of water changes and amount you need to change may increase again until your cycle has caught up. Again once you are consistently seeing low ammonia and nitrite you can add some more fish. Rinse and repeat with testing, water changes, and adding fish when safe to do so until you are fully stocked.

You can then cut back on water changes to control nitrate only. Typically you want to keep nitrate no higher than 40ppm, but I would recommend changing some water every 2 weeks even if your water test says you don’t need to.

A fish in cycle from an empty tank to fully stocked can take several months.

A good way to speed up this process would be to put a small amount of filter media from an established filter into your filter, or get a sponge from an established filter and squeeze it into your tank water. Perhaps you have a friend who keeps fish who could let you have some? This will seed your filter with the bacteria you are trying to grow and speed up the process.

Another option is bottled bacteria like Dr Tims One + Only or Tetra Safestart. These products wont instantly cycle a tank as they claim but in a similar manner to adding established filter media they can seed your filter with the bacteria you are trying to grow to establish your cycle. These products are hit and miss as to whether they work at all, but are an option if established filter media isnt obtainable and may speed up the process from several months to several weeks.
Just a further note.

Is there something wrong with your tap water? Why the bought pre-conditioned water? Most people manage just fine with tap water and dechlorinator.
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