Uh Oh! First Issues With New Tank

[Adalii]

So I have this 10 gallon tank that a friend was getting rid of, so I took it. I cleaned it out really well, and let it cycle for a few weeks(well more than a few but...you get the point). I then decided to get a few fish, so I ended up with a dwarf gourami, three emerald green cory cats, and five neon tetras. I have been planning on upgrading the tank but for now everyone has been really happy...
 
 
until today.
 
This morning I got up at the usual 6am and fed the fish, and also turned on the light. Everyone seemed fine, however when I got home at 9:30 pm I noticed my fish were pale and gasping for air. They weren't moving around too much either(moreso talking about my three cories) and I am really worried about them.
 
My tank is kept at 76-77degrees with a nice heater, has never overheated or failed to heat before. I checked my water and everything was normal for a freshwater tank, I can give exact numbers if needed, I have not done an 100% water change yet, however I did a 25% water change several days ago(I believe five days ago). I always put dechlorinator in the water and leave it to sit a minimum of four days before adding it to my tank. I recently have added a few bulbs in an attempt to grow some live plants, and have planned on purchasing some established live plants to add to my tank.
 
I would love any/all advice you can give me! This is my first tank that doesn't just hold betta fish, and I really am concerned!
 
 

Oh and I have owned the fish for about a month now.

 

[sawickib]

Having the exact water parameters would be helpful, ammonia, nitrites, nitrates and pH.
 
The tank is very over stocked with fish that need bigger tanks from the start, so id bet your dealing with some ammonia problems.
 
You should be doing 10-25% weekly, but with an overstocked tank such as yours id do 50% weekly, but you really need a larger one or rehome your neons, cories and gourami.

 

[b3cca]

No matter what the test kit says, any signs of trouble I would firstly do a large PWC right away.
No need to let your water sit for 4 days if you use a dechlorinator you can add it right away no problems.
 
sounds like a nitrite spike to me, but if not, then obviously somethings wrong so get some fresh water in there 

 

[eaglesaquarium]

I agree with the diagnosis of either ammonia or nitrite. You said you 'cycled' the tank, but did you add ammonia to the tank during that period to allow the proper bacteria to grow? Large water changes are in order now to help the fish through the crisis.

Please provide specific information regarding the ammonia, nitrite and pH.

 

[vespabloke27]

i agree .. do a water change and keep an eye on them.

 

[the_lock_man]

I agree with the diagnosis of either ammonia or nitrite. You said you 'cycled' the tank, but did you add ammonia to the tank during that period to allow the proper bacteria to grow? Large water changes are in order now to help the fish through the crisis.

Please provide specific information regarding the ammonia, nitrite and pH.

 
What he said.

 

[AeonMapa]

what filter do you use? did you recently add plants?

 

[Ch4rlie]

Not sure, you make no mention of how you have actually cycled this tank, did you cycle following this article?
 
http/www.fishforums.net/index.php?/topic/421488-cycling-your-new-fresh-water-tank-read-this-first/