How long to let 20 gal tank cycle before adding fish?

Clumsical and No Cure understand what is going on here.

There is an ever increasing amount of misunderstanding about what cycling is.

There are lots of things going on in a newly set up tank. These all get mishmash-ed together as cycling. The first three below are not cycling but they are important.

1. New tap water has chemicals in it to kill bacteria that enter the piping system that brings water into your house. Those are usually chlorine and chloramine. You use either a binding chemical that neutralizes these two chemicals, or you use an inline carbon block filter to remove the chlorine, chloramine, and any odors, tastes, organic colors, and metals such as copper that are dissolved in the tap water. This is taken care of instantly whichever of the ways you choose to use.

2. Tap water especially in cold weather has atmospheric gasses and carbon dioxide dissolved in it. As the water warms up to room temperature or higher with a heater, the amount of gas it can hold is less and bubbles form on everything in the aquarium. This usually takes overnight.

3. To adjust your heater so that it is maintaining the desired temperature you may have to tweak the setting up or down and then wait to see if the new setting is correct. Getting the temperature just right and being sure the heater is holding the temperature can take two or three days.

4. Cycling is about nitrification bacteria. There are two steps and two different jobs done by separate types of bacteria. Bony fish produce ammonia as waste instead of producing urea as most land animals do. The ammonia is excreted from their gills, not their kidneys. Fish that do produce urea in their kidneys do not excrete it into the water, but instead retain it for life in their blood. This high level of urea in the blood serves the fish as an osmotic barrier that prevents salt from the aquarium water getting in to the fish's body and swelling its tissues. Unless you have a marine shark, marine skate or ray, or a coelacanth in your tank, you have the ammonia producing type of fish.

The cycle cannot start until a fish is in the tank or you substitute a constant supply of ammonia to the tank. Someone who never bothered reading the article introducing the idea of "fishless cycling" decided that a dead fish or rotting fish food would work to supply ammonia. False of course. All that would do is supply nutrients to harmful fungus, pathogenic bacteria, and other undesirable life such as the ones that produce sewer gas (hydrogen sulphide) and coat items in the tank with a blue/black slime. There needs to be either a dosing routine or device that regularly supplies ammonia at levels that would be produced by a reasonable population of fish, or add to the tank very hardy fish such as danios, that are unaffected by high ammonia and nitrite levels.

The nitrification bacteria are found mostly on filter material from an established tank, live plants that have been in with fish, rocks, gravel, and decorations from an established aquarium, and lastly there might be a symbolic amount of them in the commercial products that claim to contain the "CYCLE" bacteria.

Killing off all of these essential bacteria by boiling rocks, drying out equipment and totally replacing filters or filter media is beyond words. All it would do is kill off what would be needed for a healthy aquarium. If there were some disease present, very few diseases would be affected by this "cleaning" and in the absence of the "good bacteria" the ones that perform nitrification, those diseases would be given a strong help in overcoming any fish later introduced to the tank.

Your 20 long is big enough for one globe bodied goldfish, if you add extra filtration. My favorite with goldfish is a Berlin or tray style wet/dry filter in a sump under the tank or remotely plumbed in from another room.

I would rather see you start your tank with zebra danios.They are interesting, hardy, and will take the tank through the establishment of the nitrification cycle. Remember nitrification is a process, like vacuuming your rugs. It is always getting done over again. Establishing the cycle only means it has been set up once. You have to keep it intact by never cleaning more than half the gravel in the same week, never rinsing or replacing more than half of the filter media in one week or you will remove too many of the good bacteria and cause ammonia spikes and nitrite spikes all over again.

I can't imagine who told you to do all of those things. You just uncycled everything.

Sorry, but goldfish get way too big to put two in a twenty gallon. If you're getting a fancy goldfish, one can live in a 20 gallon happily, but if you're getting a comet, not even one will do.

Anyways, if you plan on doing goldfish, you'll need to have a filter that works to twice the capacity of the tank (meaning one that will keep a 40 gallon tank well cleaned) because goldfish are very dirty.

After that, goldfish are generally pretty hardy. Your aquarium isn't going to cycle without an ammonia source, so just add a goldfish.

OR you could do a better option, buy a heater, and have a tropical tank. IMO, it's silly to run a 20 gallon tank for one fish.

Forget goldfish they can grow 2ft long and will need 75 gallons minimum .

Get a heater and go for tropical fish unless you want to have white cloud minnows which are cold water and don't need a heater.

you need to cycle the tank first which takes between 2 and 6 weeks ,if the tank had an old established filter and you did not wash anything out you could add that to the tank ,plus the new filter and if you kept the old gravel as well that plus the old filter would have most of the beneficial bacteria in it to cycle the tank.That would mean its just about cycled .

If not then you will have to start from scratch and cycle from the beginning .

I let my filters run for 5 days before I put fish into a new tank.I'm looking to make sure that every drop of water has run through the carbon for ammonia/chlorine removal.

I've been told three days is long enough but I won't tempt the fates.

I have 3 goldfish with white cloud minnows and a sucking loach that I've had about 3 months now. I cycled the tank for a week before adding any fish, its also not necessary to have a filter, I just have an under gravel air pump and do weekly water changes of 25%. Good luck and good fish keeping.

My Experience is it takes two weeks to cycle a tank. Hey, Instead of putting goldfish put some platties, gouramies, guppies, other more interesting fish

good luck :D

A week would be good, but two evan better!!!! ^___^