Oxygen problem in my 20 gallon?

[Zolanski]

Hey Guys!

I have a 20 gallon tank with 7 neon tetras, and I recently decided to add some red cherries into the tank. All was well, until I noticed once morning when I woke up that all my tetras were gasping at the surface of the water and the red cherries were hanging on the filter as close to the water surface as possible. I did a water change and that helped for a bit, but a couple hours later they started to do this again. Yesterday where I live the temperature reached 37 degrees celcius (98F) and I read somewhere that higher water temperatures can have an effect on the oxygen levels in a tank, but this morning the weather dropped along with the water temperature and my fish are still at the water surface. Water changes seem to be the only thing working temporarily, but I don't want to stress out the shrimp or the fish.

If anyone could help me out that would be greatly appreciated!

My water parameters are;
PH - 7.0
Temp - 22C/ 71F

I use test strips for these so i'm not sure how accurate they are;
Nitrite - 0
Nitrate - 0
Ammonia - 0

I've also attached a photo of my tank

 

[SnailPocalypse]

It seems like it could e and oxygen problem is the tank cycled?If not it could be a ammonia poising problem.But maybe to be safe and airstone could help/.

 

[StevenF]

From my experience with tetra easy strips with reference solutions and multiple ways of measuring the water, The ammonia and nitrate readings are probably accurate. Last time I saw an issue like this reported here it was a high KH value cause by a rock added to the tank. Did the strips you use report a KH and water hardness value. for now keep doing the water changes and adding a air stone would not hurt. If possible take a water sample to the local fish store and ask them to test your water and verify that they use a different kit to do it. Also verify you water temperature is OK. Also if possible use a thermometer measure the water temperature at the bottom, middle, and top of the tank. The bottom might be too cold.