The reason why I asked about the transport time is based on own experiences. At the moment that your supplier put oxygen and seal your plastic bag with the fish following things will happen. The fish will both release NH3/NH4 and CO2 to the water in the sealed bag. CO2 will lower the pH in the bag and the NH3/NH4 (ammonia/Ammonia ion) complex will be more NH4 compared with NH3. This is good because NH4 (ammonia ion) is not toxic to your fish. The ratio NH4 to NO3 is mostly depended of the pH. At pH 8.5 -> NH3 is 15 % and NH4 is 85%; pH 8 NH3 around 5 % and NH4 around 95%; pH 7 -> NH3 < 0.01 % and NH4 >99.99 % NH4 is not toxic but NO3 is very toxic.
During a long transport the amount of NH3/NH4 can be rather high in your bag but because of the rising CO2 level – the pH will be <7 in the bag. The nitrogen will be more than 99.99 % in the not toxic form – NH4. The fish will do well.
What can happen when the fishes arrive home to you. I´m not saying that this is what’s happen in this case, but one thing that can happen is that you kill your fish when you try to make it as good as possible in the acclimation process. I can see in your picture that you slowly drop water from your QT to the bags. I suppose its good water with a pH around 8. Now the pH in the bag will arise and your safe levels of NH4 will slowly convert to dangerous NH3. If the amount of NH4 was high enough when you started the process – you can end up with toxic levels of NH3 in the end of the acclimation process.
What can you do to get a safer acclimation process? Here you will get 3 suggestions
- Use a ammonia blocking agent in the bag – directly after you have open your bag – and after that - use the method you use today
- Let the bag (unopen) be in your QT in order to get the same temperature. As @Maritimer suggest - you can adjust the salinity also – and after that – just put your fishes in the QT (I have to admit that I often do not adjust the salinity in these cases – just drop the fish in the tank after temperature adjustments)
- Lower the pH in your QT to < 7 with help of bubbling some CO2 in it. Use this water (with the low pH) in the acclimation process as you do today (dripping tubes). Put the fishes in the QT and start to aerate the QT. The aeration will take out the CO2 and slowly rise the pH – after 12 hours – pH is normal.
The third method I have used many times when we have had fishes with transport times > 24 hours. It’s the best method I have used but I use all three methods now and when
I´m not saying that ammonia toxification is the reason for your lost – but it can be. Why have not both got the same way – paired pair must have come from the same tank. I can be so easy that the one that die has eaten more or later compared with the other. IMO – a fish that should be transported more than 24 hour should not be given any food at least 48 (I prefer 72) hour prior to the transport.
I hope this will help you a little
Sincerely Lasse