I had 4 Giant Danios but one of them died about a week ago. Now I have another one doing the same thing. It sits in a corner breathing like it had just run a 25 K marathon. When it does leave the corner, the other 2 Giant Danios will chase it but not what I would call aggressively. I mean they are always chasing each other somewhat.

DLH

Has your tank been through the Nitrogen Cycle?

What are the Ammonia, Nitrite and Nitrate numbers?

How long have you had the Giant Danios? How did you acclimate them?

Any other tank mates?

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Make a 30-40% water change and do it again in a few days. Somethings wrong with your water quality and making a water change will help. Danios are usuallly quite hardy. Make sure your water temp isn't above 75F and you have good aeriation and filtration running.

How can you tell if a tank has been through a nitrogen cycle? I will take a sample of water to the lfs to see what the readings are.

The Giant Danio that died and the one that's sick I bought 4 or 5 weeks ago. The other 2 I've had maybe twice as long. I acclimated them as I have always done. I would put the bag that the fish came in into the tank water. After 15 minutes or so I would add a little tank water to the bag. I would do this, every minute or so, 3 or 4 times before I would release the fish into the tank.

I have noticed now that the sick Giant Danio will chase around like he's trying to get away from something and then rubbing himself on plants. Also I've now noticed that other fish, although they don't seem to be stressed out, are rubbing themselves on the plants.

DLH

The Nitrogen Cycle is what you have to let your tank go through when you set it up, in order to be able to keep healthy fish. (How long has your tank been set up and how long have you had the fish in it for?)

You need a source of ammonia - some people do a fishless cycle and use straight ammonia (there's a sticky on the forum somewhere on how to do that.) Others will use a few hardy fish for cycling, like Danios, and their urine is the ammonia source.

Cycling with fish takes around 6-8 weeks. Bacteria has to build up in the gravel and filter media that will convert ammonia to nitrites and then nitrites to nitrates. You take the nitrates out with partial water changes each week.

During the cycle, you should not be vacuuming the gravel or rinsing anything in the filter, as you are trying to build the good bacteria up.

It is not uncommon to loose fish, or have sick/stressed fish if you are using fish to cycle, as the ammonia and nitrite are very toxic to them.

Test your water. If the ammonia or nitrIte are at 1ppm (or close to it) you need to do a 25% WC. If it's higher, then do a 50% WC. NitrAtes will start to show at the end of the cycle. Every established tank will have NitrAtes, as they are the end product of the bacteria conversions. As long as Nitrates are under 40ppm (prefereably under 30ppm) you are fine. As I said, you take a big chunk of those out at Water change time. Once your tank is fully cycled, it should read: 0ppm Ammonia, 0ppm Nitrites and Xppm Nitrates (under 30-40ppm).

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The tank was set up early last spring. I did a 50% water change yesterday.

I bought a test kit today. Here’s what I got.

Nitrate 20
Nitrite between 0.5 and 1.0
Hardness 150
Chlorine 0.0
Alkalinity 80
PH 7.2

How do I test for ammonia?

DLH

You need an ammonia test to test for ammonia. If it didn't come with the master kit then you'll have to get it separately.

Since your NitrItes are between .50 and 1ppm, I'd do a 25-30% WC now. (What I'm not understanding is why, since your tank was set up last spring, you're getting NitrIte readings.......

What size is the tank? What fish are in it (and how many)? Have you added a bunch of new fish recently? Have you changed all the filter media at the same time?

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I have a 55 gal. Right now I have 1 eleven inch common Pleco, 1 five inch bushy nose Pleco, 1 large black veil angel, 1 Cory, a couple of Ottos, about 15 Black Tetras, about 15 Red Eye Tetras, 3 Giant Danios, and about 20 H. Rasbora. I know I have to many fish for that size tank and I have to be sure I use life support methods to keep them healthy. I've done that for many many years without having a problem. The only fish I've added in the past month were 4 Black Tetra about a week ago.

I have an Aqueon 55 filter. When I changed the water Sunday I rinsed the filters under a faucet. Was that a no no?

To make sure I was reading the test strip correctly I took a water sample to the lfs. He said that all the readings were fine including the ammonia. When I told him about the fish rubbing themselves on the plants and rocks he suggested I add salt to the water. Of course I didn't right it down and now I'm not sure what amount of salt he said to use. Does 1 tablespoon per gallon sound about right?

DLH