I hope you have chance to see this before you go away for the weekend. I read your other thread also. It seems to me that when the fish have some breathing problem without the symptom of disease usually mean the tank have less oxygen or more harmful gas than adequate condition.
Of course, it would help if you can list the size of the tank, stocking level(what fish and how many.,etc.), plants(since they give off oxygen), temperature, ph, so on. You might have too many fish.
Even with those information sometime it is tough to pin point the problem but without almost impossible but some guesses. But anyway, water change should help but I would do more than 20~30% but more like 50 or even 75%. Of course, water parameter should be close, temperature, ph,.etc. And if you have some air pump, it may benefit to put it to use with air stone or even extra filter(sponge, corner) can be used with airpump. Even without those things, you can stick in the airtube in the tank. Just try to stay it in the lower part of the tank so it agitate the water to help gas exchange.
Well, those things I mention would not hurt the situation but help. Good luck and hopefully no more premature death in your tank.
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