how long should a fresh water tank be set up before adding fish?

im an helping a buddy set up a 72 gallon fresh water tank and was wondering how long it needs to be going before we add fish

Too long...it can take 6-8 weeks before you can have a fully cycled tank.
That is if everything goes right. Or you can do short cuts

You can put 30 gallons worth of treated fresh water in the new tank, aerate it well, then donate the other half of cycled water from your tank or any established tank, and move some of your filter media to his filtration system. Then add some fish as bio-load and see if the filtration system sustains them. If they do well, add some more after two weeks.

cool thanks

IMO you can get that sized tank cycled in 2-3 weeks by using ammonia to cycle it..

i got my 55gal fully cycled in 10 days by doing a fishless cycle. just pure ammonia

I got so many tanks I don't even cycle any of my new tanks. I always used the method I mentioned above. Instant!

You can add fish immediately to a brand new tank without any bacteria supplements if you're commited to several water changes. I've done it many times. You just have to do very frequent water changes anytime you get any high levels. I'd say about 25% dailey water changes and the tank will be just fine. Again the heavier you stock the tank the heavier you'll need to be with your water changes... the tank will cycle and you may not even know it!
How do you think they set up these monster tanks at ACA and stock them so heavily with fish (in brand new tanks)? Water changes water changes and more water changers! Again wait to add fish after the tank cycles if you're not commited to water changes!
JB

Most importantly ,very little feeding! Why do the major water changes if you
keep dumping food in the tank!

25% isn't a major water change but it's enough to keep the "bad" levels down in the water if done daily. I agree feed a less than you normally do but you don't have to feed "very little" if your doing the partial water changes. Keep an eye on the fish, their behavior patterns are far better indicaters of problems than chemical tests will ever be! Happy fish = happy water! Sickly fish = sickly water conditions!
JB

my method for a brand new tank.
1) goto my lfs and get a whole mess of feeder guppies, a few dollars worth (they serve the same purpose as canaries in a cave mine).
2) make sure to ask them if they can give me some of their dead fish (if they know you, they will oblige you with them for free, as they should).
3) get about 30-40 ghost shrimp.
4) ask for the dirty cruddy water from the substrate from one of their sales tanks, the nastier the browner the water the better.
5) see if you can get some pond snails or malaysian trumpet snails (just a few is all youll ever need) and they ought to be bloody free unless your lfs hates you.
6) *optional* see if you can get gut-loaded earthworms. i cant say i trust the ones from the backyard; risk of chemical contaminants and all.

Lastly, dump all this stuff into your tank and feed your tank(a table spoon of food every other day). if anything should happen to die, just let it rot in the tank.

after 2weeks begin testing your water quality weekly.

after 4weeks start do a water change

i cycle my tanks for 6-8 weeks before i add any fish i care about dying.
only add 5-7 new fish to the tank per week, use discretion and common sense on the fishes sizes and temperment that you are adding. least aggressive 1st, most aggressive should be the last fishes you add.

What I do is take a brand new tank...
Add substrate (used is better) but new will work.. Then add the water and use a dechlorinator. Get a used filter from an up and running tank if you have one. They buy a new filter and put on the old tank. That is more than enough bacteria (seed) to start the new tank. Add the fish immediately (day 1) and then do 25% water changes until you get the tank cycled. Adding dirty water and dead fish is up to you but it's a bit smelly and nasty! Especially if you can add regular fish and do just fine. By the way I've had over 100 tanks at one time up and running so I have some experience with adding new tanks!

JB

Remember , this is a closed system . Watch the food going in, Currently running approx
2000 gallons of water. I never have tanks going thru a cycle . Use already age water and age filter, I use no gravel. Water changes are very important , but the the amount of unnecessary food will cause major difficulties!

There are many ways of doing this but make sure not to discourage your friend with doing massive water changes. Makes it look like there is too much work involved. Simple 2ppm of pure ammonia every other day with testing can cycle a tank in 13 days. No fish harmed in the process and less water changes. After you see the nitrates in the readings and it gets rid of the ammonia in a 24 hour period the tank can be fully stocked depending on the fish. I have done this for many freshwater fish. You can speed up the process by adding some bb from one of your established tanks. If you get ammonia or nitrites over 4ppm do a 50% wc and and skip a day of adding ammonia . Once it gets back to 2ppm go back to dosing and testing. This can take a while but if done properly it can be done in under two weeks. I know testing water is a bit of a hassle and yes frequent water changes replace frequent testing. Some tanks I haven't tested in months due to frequent water changes. Just make sure to test tour tap water before water changes.