I'm trying to cycle this tank with fish. I have 2 guppies in there and a zebra damio. It's been three days since they went in the tank.

Ammonia, nitrate and nitrite are all at 0. Ph appears to be at 7.8 or 8.0. (This may be a problem that I'll have to address tomorrow.)

The male guppy is hiding in the cave decoration, then comes out and hangs out under the leaves of a plant. He seems like his gills are working really hard, and the other two fish are apparently fine.

My guess is that he may pass, but I was hoping someone would know if this is a symptom of something else, etc.

What tank size and filter?

It could be stress. How did you acclimate the fish before putting them in the tank?

Well, he apparently was looking for a place to die. Finally disturbed the cave decor and a dead fish was inside. :/

For the sake of discussion, I hung the bag inside the tank for about 30 mins, adding some tank water to the bag water after 10 mins.

What are you using to test your water?

If the pH is truly that high, that could have been the culprit. Guppies don't particularly like water above 7.5 for any length of time, and combined with the cycling process that's probably what did him in.

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Using the API master kit to test the water. I'll have to hit the LFS and grab something to normalize the pH after work.

Don't use ph down products, they aren't very safe for your fish. How big is the tank?

Ten gallons. This was a starter tank. And it's odd because it seems as though there is no cycle started, or I have a magically cycled tank.

I set up the tank on Sunday. I used 5 gal purified water 5 gal tap and water treater + stress coat, etc.

I then (before I found this site) added fish on Monday night using the acclimation method described above as suggested by the guy at my LFS.

Last night (Wednesday) I tested the water and everything read at 0 (ammonia, nitrate, nitrite), but the pH seemed high as described above.

I would have thought that I'd see some different values in the water by now, especially since I added the bag water from the LFS to my tank when I added the fish.

Ammonia could take a few days to show up, but it will. Not quite 3 days yet for your fish in there. Fish that die a day or two from the lfs, I usually account to stress. These fish are already stressed enough during the initial move to the store. Some fish take 2-3 days before they start acting, or at least what I would call acting normal.

My damio finally discovered my cave. Hurrah. Bonus points for darting in and out.

It's kind of funny, my daughter reacted to the death of the guppy by saying, "Can we get more fish now?"

I'm the one who feels bad.

In other news, pH seems to have dropped and quite possibly I'm seeing trace amounts of ammonia.

+1

Guppy aren't good for cycling a tank, corydoras are the best.
Manage your freshwater aquarium, tropical fishes and plants: Nitrogen Cycle for Dummies

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Is he showing any other signs of stress, besides hiding and rapid respiration? How do his fins look? Is he flaring his fins at the other guppy at all? Are his fins clamped? How's his color?