3 Dead Already :( They're Suffocating Help!

[TwoTankAmin]

I doubt you fish are gasping due to the reading of .5, I think that is likely coming down from higher. What is your ammonia?
 
Even with nitrite poisoning if you have no dechlor you can not do large water changes- that will almost certainly kill the fish. Nor will aeration help, the problem is not lack of oxygen.
 
So there are some alternative to get the fish through the time of getting more dechlor which should be under 24 hours.
 
Add salt- this mitigates the effects of nitrite. I didn't see a tank size so will give dose for US gals an id needed convert to liters.
 
remove water from the tank to a clean container where you will add the salt to dissolve it- then pour the water around the tank to minimize impact.
 
Dose 1 teaspoon for every 3 US gallons of water. Dose this now and in another 12 hours you can add that amount again if needed. The problem with adding salt which will help is it will also affect the hardness of the water by raising it. Raise it too much and too fast and it can kill fish. So what you are doing is breaking up the dosing.
 
However, if after adding the first salt, you may watch the fish and see no improvement after 30-60 minutes. In that case you will have to risk another dose right away.
 
You can use table salt if that is all you have, better is kosher salt with nothing added. be sure the salt has nothing added - Iodized salt will even do in a pinch.
 
Now you are expected to be doing 2 things in the next 24 hours, get dechlor that is not stress coat- I am not in favor of adding aloe vera to water where fish are having breathing issues. When the fish recover you can switch back. Also get and a new thermometer. Then do a 50% water change and get the temp right.
 
Also- you can put your hand into the water to get an idea if it is very warm. You can cool it in own of two ways- one- fill a container with tank water, put it in the freezer and when solid remove- run under tap water to remove it and put it into the tank. Two- place ice cubes into a baggie that seals, float the bag in the tank. however I am thinking this isn't may not be issue, its the nitrite.
 
Now when done with the emergency measures, Google "Brown Blood Disease" to understand what is going on with your fish. You may also want to Google "Brown Blood Disease + salt"

 

[the_lock_man]

TTA, the tank is a 60l.
 
OP, you need to get 300mg of salt into the tank to mitigate the effects of the nitrite.

 

[Jmbbf]

This morning I woke up and had lost another 2 fish (5 in total) I definitely think this was because the water was too hot as the remaining fish are all fine now all neons have got their colour back and seem to be swimming about happily as usual. I've purchased a new thermo and temp is perfect. I didn't want to add salt as I wasn't convinced it was the nitrites and was the temp. Will still be keeping a strong eye on them all day.
Would it be ok to fast them for today to get over the trauma?
Thanks again everyone for your advice.

 

[the_lock_man]

I disagree with your diagnosis, but hey, all's well that ends well.

 

[TwoTankAmin]

I also do not agree. Heaters contain a thermostat that is supposed to turn them on and off automatically. For your heateer to keep heating a tank above the level to which it is set means it is probably broken. If it is broken you need a new one as the problem will likely recur.
 
On the other hand you lost 5 lost 5 fish. If it was the heat you would have seen a completely different behavior. When subject yto rising heat levels that become lethal fish will behave in a manner easy to spot. First they will go listless and then they will have convulsions and then they die. If they are suffering from nitrite poisoning, they will be gasping at the surface and adding oxygen will not help. That is why turning your air pump on full did not help with the breathing even though it may have helped with temperature some.
 
Bear in mind that fish are all different. One dies at X level of nitrite or ammonia and its tank mates do not all die at the same time. Individual differences account for this. Otherwise all your fish would be dead. Since, by the time you reported things here, the nitrite was down to .5 ppm, it likely cleared up fast from there. That still doesn't address the question of how high it actually got. For my money the problem was not temperature, although that could have exacerbated things.
 
Glad to hear its back under control.