If you kept the filters alive, there should be no problems. The tank will be ready ofr fish the same day as far as the water goes, even if you take water from the tap and dechlorinate. The only possible problem is that the bacteria has died in the filters and the tank needs to cycle. Since you really need to add the fish asap, you will have to watch the water parameters carefully, for ammonia and nitrites. Plan on doing lots of water changes until the tank gets established. The old tank water is of no real benefit to you, although adding some will not do harm.

 

Do you want to keep the fish? If not, why not see if the LFS will give you a credit for them?

You can also get a test kit to see, I think you'll still need some time to let the bacteria establish themselves in the whole tank.

 

Most LFS won't give you too much or anything or might refuse to take large oscars and common plecs. The best you can hope for is a few bucks each.

New water is totally fine. It could all new water, as long as it's filtered or treated to be safe. Good luck with the big tank!

 

Here's an update:

Went and had my water tested earlier. pH is good, as is everything else except nitrates and nitrites are a little bit high. Not "dangerously" high, but still high. I have both filters running and it looks pretty good. Should I risk it and put the fish in?

Oh, and one other thing. I live in the US, but I joined this forum because I had received some valuable information from it in the past and knew that you all would be able to help me.

I went and had my water tested earlier at a pet store, and while I was there, there was a lady who offered me another huge pleco that had outgrown her tank. I always loved how the massive plecos looked in the huge aquariums, and soon I will have two!

 

I don't think you need to worry about pH too much. If ammonia is 0 and nitrite level is up, the tank is definitely cycling. I'd say wait for at least 3 more days or a week before adding fish. Of course, testing the water condition before adding fishes is recommended.

Why not purchase water test kit for yourself? It'd be cheaper than going to pet store all the time to check your water samples. I'm sure you'll need to check water quality time to time even after the tank fully cycles.

 

There is something out of kilter if you are getting nitrite and nitrate readings in a tank with no fish. The water you added from the old setup would have to have been loaded with both for you to have readings in a new setup. You obviously can't keep those fish in a 20 for any length of time without incurring problems. It would be better to move those fish into the new tank than leave them in the 20.

 

There is something out of kilter if you are getting nitrite and nitrate readings in a tank with no fish.

You can get ammonia/nitrite/nitrate without fish. Any organic material once decomposing will create nitrates as an end product.

Probably has mulm in the substrate which registers a nitrate reading, which wouldn't be surprising with the tank buster fish involved.

 

Here are a few pictures of the aquarium and the fish. Everything is going good now. Fish are happily devouring any/all food given.

 

Truly beautiful. Those are awesome fish.

I would be concerned about the high nitrite reading. As far as I know, a high ammonia level can be offset with ammo chips but the only thing that can offset a high nitrite reading is a water change, other than a cycled filter of course.

Please correct me if I'm wrong.

 

if you have a tank allready filled up swap some of the old bacteria rich media to the new filters should kick start it fast