I bought 7 Glofish Skirt tetras 3 weeks ago and today was the first time I've changed 25 - 30% water for them in 10G (38L) aquarium. Replaced water was tap water warmed for few hours and treated with API Quick Start as per water change instructions. 10 minutes after the change all 7 tetras lifted to the surface and started swimming there like gasping for air. It's been like this for 2-3 hours. Before the water change they never swam at surface, they were happy and playful. I have water filter, heater, air pump dispersing air in the water. I measured water quality with strips and all 7 parameters look good, better than it was before water change. Please advise what does this behavior mean.

Update: in a couple of more hours all 7 fish are dead. I still do not understand what went wrong. Something poisonous for them was definitely in the water that killed them in few hours, and I do not understand what exactly. Water parameters per Tetra Easy Strips:

  • Nitrites: 0.5 ppm

  • Hardness: soft

  • Chlorine: 0

  • pH: 7.2 - 7.6

  • KH: 80 - 100

I think as it was my first water change could be something poisonous in new plastic tools that I used, like pump tube or bucket. Though I rinsed them with warm tap water, something poisonous still might had been left.

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  • 2
    what color was the fishes gills when they was still alive,this can give a indication of what went wrong. Feb 5, 2018 at 7:50
  • I did not pay attention to their gills color, sorry
    – YMC
    Feb 5, 2018 at 14:20

3 Answers 3


When fish goes to the surface of the water there is some thing wrong, like the lack of oxygen or the presence of poisonous substances in the water.

The water test you are using is not reliable and it does not measure ammonia, so it is better to use a liquid type of test kit.

The API Quick Start is a bacteria mix and is used when one cycles the tank, a little about this is in an article on FishLore.com.

The API Quick Start does not remove chlorine from the water, so you have to get another remedy for this.

Reasons for the fish going to the surface of the water:

  1. Ammonia or nitrite in the water.

  2. Lack of oxygen or excess of CO, CO2 in the water.

  3. Chlorine in the water other types of chemicals present in the water like heavy metals or if you uses air fresheners in the room (very toxic for fish and water-living organisms).

  4. Toxins from plastic used in the tank or equipment used when you change the water (hot water makes plastic release a larger amount of toxins), so only use equipment made of plastic approved for food use.

A little about chlorine: if present in water used in your tank, chlorine will kill the bacteria so you might end up with new tank syndrome and have a ammonia and nitrite spike in the water.

Your question is not easy to answer, but my theory is an ammonia spike have happened in your tank, you will see a nitrite spike in your tank in a couple of days if I am right.

  • 1
    Thank you for your response. I used Betta Conditioner to neutralize chlorine, I believe it's Ok for Tetra too. Test strips did not measure ammonia indeed. However could the ammonia spike happened in minutes or even seconds and kill fish in 3 hours? I'm recalling the fish first reaction when I filled tank with 30% new water: they all rushed to the aquarium wall hitting the glass like trying to escape, I think they felt the wrong water conditions immediately. And then 10 min later they are on a surface gasping for air, 3-4 hours they're all dead.
    – YMC
    Feb 5, 2018 at 15:34
  • 1
    it can be hard to find the reason for why the fish died,amonia can build up in a few hours and clorine might be neutrlized in a short time so the evidence might be gone when you tested the water.you might take some water back to the shop for testing and if it shows up as ok you can buy some cheap fish and put them in your tank to see if they survive. Feb 5, 2018 at 17:33
  • 1
    the declorinator you have used is ok,but next time you change water you might want to treat the water before you add it to the tank and it is smart to fill containers with water and let it rest overnight before you use it. Feb 5, 2018 at 17:49

This sounds very much like chlorine poisoning, if only because the effect took hold so rapidly. The behaviour can be similar for ammonia poisoning, but I wouldn't expect ammonia poisoning to become a problem in the timespan of minutes as you described. Fish with chlorine poisoning suffer damage to the gill membranes, and so breathe at the surface in order to boost their oxygen consumption.

API Quick Start is not a dechlorinator, so is the wrong product for periodic water changes. What you should be using is Stress Coat or another dechlorinator, if you're replenishing using tap water.

  • I used Betta Conditioner, not sure if it's fully compatible with Tetra GloFish, and I think I might added too little of it. However my test strips which I used 10-20 min after the water change shown white color (zero) for chlorine indication.
    – YMC
    Feb 5, 2018 at 16:11

Certainly it was "chlorine" or equal .Don't buy anything. Put tap water in containers like ( empty , rinsed -NO soap) plastic gallon milk bottles . Let them sit a couple days at room temperature . You now have suitable water, at least it has worked for me for 70 years . PS; I don't like the modern stained fish , natural fish look just fine.

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